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MODERN 

Electrical Construction 

A RELIABLE, PRACTICAL GUIDE FOR THE 
BEGINNER IN ELECTRICAL CONSTRUCTION 
SHOWING THE LATEST APPROVED METHODS 
OF INSTALLING WORK OF ALL KINDS AC- 
CORDING TO THE SAFETY RULES OF THE 

National Board of Fire Underwriters 



By 

HENRY C. HORSTMANN 

\\ 

and 

VICTOR H. TOUSLEY 

Authors of ^^ Modern fViring Diagrams and Descriptions^' Elec- 
trical fViring and Construction Tables^''' ^''Practical 
Armature and Magnet Winding^'''' ^^Electricians 
Operating and Testing Manual y^' Etc. 



MiixBtvnUh 



Third Edition — Revised and Enlarged 




CHICAGO 
FREDERICK: J. DRAKE & CO., PUBLISHERS 






Copyright, 1904 

BY 
HORSTMANN AND ToUSLEY 



Copyright, 1908 

BY 
HoRSTMANN AND ToUSLKY 



Copyright, 1911 

BY 

HoRSTMANN AND ToUSLEY 



rD 



^ 



C;ci.A2soo7r, 



PREFACE 



In this volume an attempt is made to provide the beginner 
in electrical construction work with a reliable, practical guide ; 
one that is to tell him exactly how to install his work in ac- 
cordance with the latest approved methods. 

It is also intended to give such an elaboration of "safety 
rules" as shall make the book valuable to the finished work- 
man as well. To this end the rules of the ''National Electrical 
Code" of the National Board of Fire Underwriters have been 
given in full, and used as a text in connection with which 
there is interspersed in the proper places a complete explana- 
tion of such work as the rules may apply to. This method of 
teaching and explaining practical electricity may at first glance 
seem somewhat haphazard, but it resembles very closely the 
actual method by which the most successful, practical work- 
men have learned the trade. It is thought that explanations 
pertaining directly to the work in hand will be more deeply 
considered and more likely to be fully comprehended than 
explanations necessarily more abstract. 

It should be noted that, while the rules published in the 
"National Electrical Code" are standard and work done in 



conformity with them will be first-class, several of the larger 
cities have ordinances governing electrical work which con- 
flict in some details with these rules. Workers in such cities 
should, therefore, provide themselves with copies of these 
ordinances (usually obtainable without charge), and compare 
them with the rules given in this work. It is necessary for 
the electrical worker at all times to keep himself posted, for 
safety rules are liable to change. 

The tables concerning screws, nails, number of wires that 
can be used in conduit, etc., are especially prepared for this 
volume, and give to it particular value for practical men. 

The Authors. 



PREFACE TO SECOND EDITION 



The favorable reception which the first edition of this 
work has received at the hands of electrical workers generally 
has induced the authors to prepare this, the Second Edition. 
Considerable new matter, notably a section on Theater Wir- 
ing, has been added. All the necessary alterations and addi- 
tions have been made in the text to conform to the latest 
issue of the National Code, together with the required explan- 
ations and illustrations. Other sections have been extended 
and the whole work has been carefully gone over and re- 
vised wherever the progress of the art has made it desir- 
able. 

The Authors. 



PREFACE TO THE THIRD EDITION 



In a work of this kind it is of prime importance that it be 
kept abreast of the times. Safety rules are liable to change, 
m fact must do so to adapt themselves to the steadily increas- 
ing number of new inventions and devices brought upon the 
market. 

This woi^ having found sufficient favor in the eyes of many 
instructors to warrant its adoption as a text-book, is to be 
revised and new matter added as often as notable changes in 
methods of construction or safety rules make it appear de- 
sirable. 

The latest additions and modifications of the "National 

Electrical Code" are contained in an appendix which should 

be consulted. New illustrations are inserted in the liody '>f 

the work as needed. 

The Authors. 



CHAPTER I. 
The Electric Current. 

It is quite customary and convenient to speak of that 
agency by which electrical phenomena, such as heat, light, 
magnetism, and chemical action are produced as the electric 
current. In many ways this current is quite analogous to cur- 
rents of air or water. Just as water tends to flow from a 
higher to a lower level, and air from a region of greater 
density or pressure to one of lesser density, so do currents of 
electricity flow from a region of high pressure to one of low 
pressure. Currents of electricity form no exception whatever 
to the general law of all action, which is along the lines of 
least resistance. It must not be understood, however, that 
electricity actually flows in or along a conductor, as water 
does in a pipe, and the analogy must not be carried too far, for 
the flow of water in pipes is influenced by many conditions 
which do not influence a flow of electricity at all, and vice 
versa; there are conditions surrounding conductors, which 
influence the flow of electricity which do not affect the flow 
of water. 

Above all, let it be understood that electricity is not inde- 
pendent energy, any more than the belt which gives motion 
to a pulley is. In other words, it is not a prime mover, it is 
simply a medium which may be used for the transmission of 
energy, -just as the belt is used. To use electricity as a 
medium for the transmission of energy, it must be, we may 
say, compressed, or, to use a more properly technical expres- 
sion, a difference of potential or pressure must be created in 
a system of conductors. This is very similar to the use of air 



8 MODERN ELECTRICAL CONSTRUCTION. 

for power transmission; this must also be compressed so that 
a difference of pressure exists within a system of piping. 

It is the flow of electricity or air which takes place when 
switches or valves are operated and which tends to equalize 
this pressure, i. e., flow from high to lovv pressure, that does 
our work. The real energy, however, (so far as we are con- 
cerned), to which we must look for our initial motion in 
either case is derived from the coal which generates steam; 
or, in the case of water-driven machinery, the rays of the sun 
which evaporate water, allowing it to be carried to higher 
levels, from whence it flows downward over dams ar.d falls 
on its way back to the lowest level. In the battery, the real 
energy is that of chemical action, which is transformed into 
electrical energy. 

The flow of current can take place only in a system, of 
conductors which usually, for convenience, are made in the 
form of wires. The current for practical purposes m.ay be 
considered as flowing along such wires only. It is not, how- 




Figure 1 

ever, necessary that these wires should be of any particular 
size, or consist all of the same material. In an electric bat- 
tery, part of the circuit consists of the liquid contained within 
the battery; the rest being made up usually of wire. In an 
incandescent light circuit part of the circuit consists of the 



ELECTRIC CURRENT. 9 

lamp filament (usually carbon), while the balance of the cir- 
cuit consists of copper wire. 

The flow of current is also said to have a certain direction ; 
that is, it is noticed that many of its effects are reversed when 
the terminals of the battery are reversed. Referring to Fig. 
1, which shows a battery of three cells, the current flows from 
the copper element at bottom of jar 1, along the wire to the 
zinc element at top of jar 2, thence through the liquid to the 
copper element at bottom of jar 2, and from there to the zinc 
at top of jar 3, etc., and finally through the wire a back to 
the starting point. Within the battery the current flows from 
the zinc to the copper and the decomposition of the zinc gen- 
erates the current. In the wire outside of the battery the cur- 
rent flows from the copper to the zinc as indicated by arrows. 
The combination of battery and wire is known as an electric 
circuit. The current will flow in this circuit only while it 
is complete, that is while each wire connects to its proper 
place as shown. If any wire is disconnected, the current flow 
will cease. Such a circuit is said to be open, but when all 
connections are properly made it is said to be closed. 

Work can be obtained from a flow of current in many 
ways. If the current be forced to flow over a wire which is 
very small in proportion to the current carried, it will be 
heated thereby and finally melted if the current is excessive. 
This is how electric light is obtained. 

If a wire carrying current be wound many times about 
an iron bar this bar becomes a magnet; that is, while the cur- 
rent is flowing around it, the bar has the power to attract 
other objects of iron or steel. The bar if made of well an- 
nealed iron will be a magnet while current is flowing around 
it, but will cease to be magnetic whenever the current flow 
ceases. Upon this fact the operation of electric bells, telegraph 
instruments and motors is based. 

If a current of electricity flow through a properly arranged 



10 MODERN ELECTRICAL CONSTRUCTION. 

''bath," one of the plates will be gradually consumed and the 
other increased in weight. This effect is made use of in 
electro-plating, etc. If the jar contains water slightly acid- 
ulated and the current flows through it, the water will be 
decomposed and oxygen and hydrogen gas will be formed. 
This and many kindred effects are daily used in thousands of 
chemical laboratories. 

If a wire carrying an electric current be placed very close 
to another wire forming a closed circuit, a wave of current 
will ^ be induced in that wire every time the current in the 
other is made or broken, i. e., whenever it starts to flow or 
stops flowing. This fact forms the basis of the alternating 
current transformer. 

All of these facts are used sometimes together, sometimes 
singly in measuring the electric current. 

Conductors and Insulators. 

Electrically speaking, all substances are divided into two 
classes. They are either conductors or insulators. By thi^ 
is not meant that some substances can carry no current at 
all, for, as a matter of fact, there is no such thing as either a 
perfect conductor or a pecfect insulator. A current of elec- 
tricity can be forced through any substance, provided the pres- 
sure (E. M. F.) be made great enough, and there is no easier 
path open to the current. The two terms, conductor and 
insulator, are relative terms and must be understood simply 
to mean that the electrical resistance of a good conductor is 
infinitesimally small as compared to tliat of a good insulator. 
The lower the specific resistance of any substance, the better 
its conducting qualities ; the higher the specific resistance of 
any substance, the better will be its insulating qualities. 

At the left is given a list of good conductors, in the order 
of their conductivity, the figures representing the relative con- 



ELECTRO- MOTIVE-FORCE. 11 

ductivity of these metals. A list of insulators is given at the 
right; all of these are more or less affected by moisture, los- 
ing their insulating qualities when wet. 

Silver 100.0 Dry air. Fiber. 

Copper 94.0 Rubber. Wood. 

Gold 73.0 Paraffin. Shellac 

Platinum 16.6 Slate. 

Iron 15.5 Marble, 

Tin 11.4 Glass. 

Lead 7.6 Porcelain. 

Bismuth 1.1 Mica. 

Pressure or Electro-Motive Force. 

Currents of electricity flow only in obedience to electrical 
pressure. This pressure is measured and expressed in volts, 
the unit of electrical pressure being the volt. If we speak 
of water or steam pressure, we speak of it in pounds, the 
pound being the unit of measurement. In speaking of elec- 
trical pressure we refer to it as of so many volts. There is no 
direct connection between the pound and the volt, but each 
in its place means about the same thing. 

The volt is defined as that difference of potential (pres- 
sure) that must be maintained to force a current of one 
ampere through a resistance of one ohm. 

If we have a resistance greater than one ohm and wish to 
send a current of one ampere through it, we can do so by 
increasing the pressure or voltage, as it is termed, accordingly. 
The current flowing in a circuit can also be reduced by reduc- 
ing the voltage. 

The ordinary incandescent lamps operate at about 110 
volts pressure, although some are built for 220 volts. An elec- 
tric bell requires about 2^ volts (a battery of 2 cells) for 
proper operation. 



12 MODERN ELECTRICAL CONSTRUCTION. 

Resistance. 

We have seen that a flow of current always takes place 
along or in a conductor. Every conductor, no matter how 
large or small it may be, offers some resistance to this llow 
of current just as the water pipe offers more or less resistance 
to the flow of water. This resistance may be measured and 
expressed in ohms; the unit of electrical resistance being the 
ohm. The ohm is defined as that resistance which requires a 
difference of potential of one volt to send a current of one 
ampere through it. If we should desire to send a greater cur- 
rent through any resistance, we can do so by increasing the 
pressure, just as we can increase the flow of water in a pipe 
by increasing the pressure or head of water in the tank that 
supplies it. If the pressure is fixed we can S^ecrease the 
current by using a wire of greater resistance or increase it by 
using wires of lesser resistance. 

The ohm is the resistance of a column of mercury 106.2 
centimeters long (about Syi feet) and one square millimetre 
(about .0015 sq. in.), in cross-section, at the temperature of 
melting ice. 

The resistance of a No. 14 copper wire about 380 feet long 
is equal to one ohm. 

The resistance of all conductors increases directly as the 



Figure 2 

length and decreases as the cross-section increases. In Figure 
2 the resistance of the two bars of copper is exactly equal. 
Bar No. 1 having a cross-section of 4 square inches and being 
4 feet long, while bar No. 2 has a cross-section of only 1 
square inch and is only one foot long. If bar No. 1 were 



OHMS LAW. 13 

reduced to a cross-section of 1 square inch, it would become 
16 feet long and would have a resistance 16 times as great as 
that of bar No. 2. 

Current. 

The electric current is the result of electrical pressure 
(volts) acting through a resistance, and is measured in 
amperes, the ampere being the unit of current strength. The 
ampere is defined as that current which will flow through a 
resistance of one ohm when a difference of potential or pres- 
sure of one volt is maintained at its terminals. 

The ampere expresses only the rate of flow, not the quan- 
tity. Knowing the amperes if we would know the quantity, 
we must multiply by the time that the rate of flow continues. 
Ihe rate of flow is analogous to the speed of a train; unless 
we know how long the train is to maintain a certain speed, we 
have no idea how far it is going. 

Quantity in electricity is measured in coulombs. The 
coulomb is the quantity of current delivered by a flow of one 
ampere in one second. 

Ohm's Law. 

Ohm's law expresses the relation of the three principal 
electrical units to each other and forms the basis of all elec- 
trical calculations. 

This law states that in any electric circuit (with direct 
current) the current equals the electro-motive force divided by 
the resistance. The current, we have already seen, is the 
medium which does our work. Current flow, we see from this 
law, can be increased either by increasing the electro-motive 
force, or electric pressure, which causes the flow ; or by 
decreasing the resistance which tends to prevent current flow. 
Expressed in symbols it is this : I=E/R ; where I stands for 



14 MODERN ELECTRICAL CONSTRUCTION. 

current, E, for electro-motive force, and R for resistance. If, 
as an example, we have an electro-motive force (which we 
shall henceforth designate by the customary abbreviation, E. 
M. F.) of 110 volts and a resistance of 220 ohms, the resulting 
current will be 110 divided by 220 =>^ ampere, being approxi- 
mately the current used in a 16 cp. incandescent lamp at 110 
volts. Thus it will be seen that by a very simple calculation 
we can find the current flow in any conductor if we but know 
the E. M. F. and the resistance of that circuit. 

This formula can also be used to find the E. M. F., if we 
know the value of current and the resistance, since E divided 
by R=I ; I times R must equal E. If the current and resist- 
ance are known, we need only to multiply them together to find 
the E. M. F.; IXR=E. Knowing the current and E. M. F., 
we can find the value of the resistance by dividing the E. M. 
F. by the current; E/I=R. 

As a practical application of these formulas : If we wish 
to know how much current a certain E. M. F. can force 
through a certain resistance, we must divide the E. M. F. 
(volts) by the resistance (ohms.) If we wish to know what 
E. M. F. (volts) will be necessary to force a certain cur- 
rent (amperes) through a certain resistance, we need only 
multiply the current (amperes) to be obtained by the resist- 
ance in ohms. If we wish to know how much resistance 
(ohms) must be placed in a circuit to keep down the current 
flow to a certain limit, we need only divide the E. M. F. 
(volts) by the desired current (amperes) ; the result will be 
the value in ohms of the required resistance. 

Power. 

The power consumed or transmitted in an electric cir- 
cuit equals the product of the volts and amperes; pressure 
and current. 



POWER. 15 

To find the power of a steam engine, we must know the 
pressure of the steam and the quantity used ; the power con- 
tained in the water of a dam depends upon its vokime and its 
head. The power we can obtain from the wind depends upon 
Its speed and the surface we expose to it which also measures 
the quantity. 

All of these cases are analogous and similar. Power ex- 
presses the rate of doing work, thus the rate of work is the 
same whether we are lifting one pound at the rate of 100 
feet per minute, or 100 pounds at the rate of one foot per 
mmute. The unit of electrical power is the watt. It is the 
power expended in an electric circuit when one ampere flows 
through a resistance of one ohm, or when a difference of 
potential of one volt is maintained m a circuit having a resist- 
ance of one ohm. In an electric light circuit, for instance, 
as far as the power is concerned, it is immaterial whether 
each lamp requires 110 volts and H ampere, or 55 volts and 
one ampere, or 220 volts and % ampere. The power (watts) 
expended in an electric circuit is always equal to the volts 
multiplied by the amperes; thus, one ampere at 1,000 volts 
IS equal to 100 amperes at 10 volts, or to 200 amperes at 5 
volts. In any power transmission whenever the pressure 
(volts) is lowered, the current (amperes) must be increased 
or the power (watts) will fall off, and, oil the other hand, 
whenever the pressure is increased the current may be 
decreased. 

Instead of muhiplying vohs by amperes, we can find the 
power m an electric light circuit by multiplying the current by 
Itself and then by the resistance; or the E. M. F. by itself and 
divide by the resistance. 

Thus knowing the volts and the amperes, we use the 
formula E X I=W. Knowing only the amperes and the 
ohms, we may use the formula, P X R = W; and lastly 



16 



MODERN ELECTRICAL CONSTRUCTION. 



knowing only the volts and ohms, we use the formula, 
EVR = W. 

In the above E stands for E. M. F., or volts; I for current 
or amperes ; and R for resistance or ohms. 



Divided Circuits. 

Currents of electricity always flow along the paths of 
least resistance just as currents of water do. Water, it is 
well known, will not flow over the top of a mill dam while 




Figure 3 

there is an opening alongside of it through which it can flow. 
If a barrel of water be provided with two openings, one 
large opening and one small, a much larger quantity will 
flow out through the large opening than through the small. 
This is because the resistance to the flow of water of the 
large opening is so much less than the resistance of the 
small opening. 

An electric current will act in just the same way; the 
conductor having the lesser resistance will carry the greater 
current. If we know the resistances of the different paths 
open to a certain current we can determine to a nicety how 
much current will flow in each. In Figure 3, which repre- 
sents diagramatically a battery of two cells and an electric 
circuit, the resistance of the two paths, a and b, is equal to 



DIVIDED CIRCUITS. 17 

10 ohms each, and the current will divide equally between 
them. If the resistance of a were 5 ohms, and that of b, 
10 ohms, two-thirds of the total current would pass through 
a and the one-third through b. 

In all such divided circuits, the current is always in- 
versely proportional to the resistance and the simplest way 
to find the current in each is to add the resistances of the two 
circuits; for instance as above, 5 plus 10 equals 15; now 
5/15 of this current will flow through the 10 ohms and 10/15 
of the current will flow through the 5 ohms. 

To determine the combined resistance of the two wires, 
a and b, we need simply to consider them as made into one 
wire. If they are both alike, they would, if made into one 
wire, be twice as large as either one is at present, and would 
then have only one-half as much resistance as either one had 
before; for the resistance of any conductor increases directly 
as its length, and decreases as the cross-section increases. 
The combined resistances of any two conductors can be found 
by multiplying their two resistances together and dividing 
this product by their sum. Thus, again taking the value 
of a and b as 10 ohms each, 10X10 equals 100, this divided 
by 10 plus 10 equals 5, which is the combined resistance of the 
two. 

If we have a large number of branch circuits as shown in 
Figure 4, which represents diagramatically an incandescent 

GnunuB 

Figure 4 

electric light circuit of 12 lights (which is equal to 12 separate 
circuits, since each lamp really forms a circuit by itself), we 
can find the joint resistance of the 12 by proceeding as before; 
that is, multiplying together the resistance of the first and 




18 MODERN ELECTRICAL CONSTRUCTION. 

second lamp and dividing by the sum of these resistances ; next 
take the result so obtained (which is the combined resist- 
ance of the first two lamps) and with it multiply the resist- 
ance of the third lamp and divide by the sum as before. By 
repeating this operation and always treating the joint resist- 
ances already found as one circuit, the joint resistance of any 
number of such circuits can be found. Another and a very 
much quicker way consists in using the following formula : 
The joint resistance of any number of parallel circuits is 
equal to the reciprocal of the sum of the reciprocals. The 
reciprocal of any number is 1 divided by that number. If we 
have three circuits, having respectively 10, 20, and 30 ohms 
resistance, we proceed in the following way: The reciprocal 
of 10 is 1/10, of 20, 1/20, etc., the joint resistance, there- 
fore, is 1/10 plus 1/20 plus 1/30 equals 11/60, and 1 divided 
by this number which is 5 5/11. 

These methods are only necessary when the resistances 
are of different values. When all of them are alike, as is 
usual with incandescent lights, the resistance of one lamp 
needs only to be divided by the number of lamps to find the 
joint resistance. Thus, supposing each of the 12 lamps to 
have a resistance of 220 ohms, the joint resistance of the 
circuit would be 220/12=181/3. 



CHAPTER II. 
Electric Bells. 

We are now in a position to apply the electrical laws we 
have just discussed practically, and for this purpose may 
take up electric bells and bell circuits. 

Figure 5 shows an electric bell, push button and battery, 
all connected up and complete. The action of the bell when 




Figure 5 



fully connected is as follows: Pressing the push button 
closes the circuit and current at once flows from the carbon 
pole marked + through the push button to the binding post 
A on the bell frame, thence along the fine wire W to the 
iron frame-work supporting the armature, B. This frame- 



20 MODERN ELECTRICAL CONSTRUCTION. 

work is in electrical connection with B. The armature, B, 
is provided with contact spring S, which normally rests 
against the adjusting screw, C. The current now passes from 
the contact spring to the adjusting screw and from it to the 
wire wound on the magnets, M, around the many turns of 
wire to the binding post, D, and back to the zinc pole of the 
battery marked — . 

The current circulating many times in the wire wound on 
the spools of M makes the iron cores magnetic so that they 
now attract the armature B. When this armature is at- 
tracted, it moves towards the magnets, M, and carries the 
small contact spring with it, thus breaking the connection be- 
tween C and S. 

This stops the current flow and the magnets, M, are at 
once demagnetized, thus releasing the armature B, which 
flies back and again clo.^es the circuit at CS, this causes the 
armature to be attracted again and once more the circuit is 
broken. In this way the armature is made to strike the gong 
continuously while the circuit is kept closed at the push button. 
When the button is released, the circuit is permanently open 
and the bell at rest. 

In the figure there is shown only one cell, this, if a good 
form is selected, is sufficient for a new bell if the circuit is 
not long. When, however, the bell is used much the contact 
points are eaten away by the little sparks occurring every time 
the bell breaks the circuit. Dirt is also likely to gather on 
them and prevent good contact being made. Both of these 
factors add resistance to the circuit, and consequently 
lessen the current flow* 

We have seen before that the current equals the E. M. 
F. divided by the resistance, and in order to obtain the 
necessary current flow to operate the bell, we may either 
clean the contact points to lessen the resistance, or increase 
the E. M. F. by adding another cell in series with the first. 



ELECTRIC BELLS. 



21 



The latter expedient is by far the better, because it gives 
us a little surplus of power which is very useful to over- 
come variations in adjustment of the contact spring, loose 
contacts, dirt, etc. We should avoid using too many cells 
as well as not enough. If too many cells are used, there 



Q 






Of 



cczsi 



n_ 



* 



m 



Figure 6 

will be much unnecessary damage done to contact points by 
the larger sparks. 

If the circuit is very long, the great length of wire will 
also provide additional resistance. This can be overcome in 
two ways, by increasing the E. M. F. as above, or by using 
larger wires. We have already seen that the larger the wire, 
the less will be its resistance. It is common practice to use 



22 MODERN ELECTRICAL CONSTRUCTION. 

No. 18 copper wire for all ordinary distances and for single 
bells. With large bell systems, it is customary to use No. 16 
or 14 for the main wire, which leads to all of the bells and 
may be called upon to supply several bells at the same time. 
Figure 6 shows a diagram of such a system and in case the 
three push buttons are used at the same time, three times as 
much current will flow in the main or battery wire a as in 
either of the other wires. 

We have seen before that currents of electricity divide 
among different circuits in the inverse ratio of their resist- 
ances. In other words, the circuit having the least resistance 
will carry the most current. If our bell system. Figure 6, 
be "grounded" at the two points x and y (i. e., bare wire in 
contact with metal parts of buildings which are connected 
together) the current instead of flowing through the longer 
circuit and the bell, will flow through the short circuit and 
leave it impossible to operate the bells. If the contacts, at 
X and y are poor, i. e., of high resistance, only a small part 
of the current will leak from one to the other. In such a 
case, the bells may work properly, but the battery will soon 
run down and there is a strong likelihood that one of the 
wires will be eaten away through electrolytic action. To 
prevent troubles of this kind, bell wires should be well in- 
sulated and kept away from pipes or metal parts of building. 
Damp places should also be avoided and special care is 
recommended for the battery wire a, Figure 6. For further 
information concerning diagrams, etc., of bell circuits the 
reader is referred to Wiring Diagrams and Descriptions by 
the authors of this work, Fred J. Drake & Co., Chicago. 

Bell wires are usuaHy run along base boards, over picture 
mouldings, etc., in some cases they are also fished as explained 
further on. Batteries should be located in cool, dry places, 
where they are not liable to freeze, and where they are 
readily accessible as they must be kept nearly full of water 
and must be recharged from time to time. 



23 



The Telephone. 

The principle and action of the Bell telephone can be best 
explained by reference to Figure 7. In this figure, A repre- 
sents the transmitter, and B, the receiver. The essential 
parts of the transmitter are: the diaphragm, a; an electric 
circuit, containing a battery, h, and consisting of the wires, 
c, c^ and partly wound upon an iron core, d. 

This electric circuit, it will be seen from the figure, con- 
nects with one pole to the diaphragm, a, and with the other 
to a small metal plate, e. Between the diaphragm, a (which 
is a plate of very thin iron), and the plate, e, there are many 
small pieces of carbon which complete the circuit. When 
now a party speaks into the mouthpiece of the transmitter, 





Figure 7 

the sound waves cause the diaphragm, a, to vibrate; the rate 
of vibration and character of the vibrations being an exact 
duplication of the voice speaking into it. These vibrations 
cause the small pieces of carbon between the diaphragm and 
the back plate to be alternately compressed and allowed to 
expand. Now the resistance of these carbon pieces is de- 
creased as they are tightly pressed together, and again in- 
creased when the pressure is released. Therefore the cur- 
rent of electricity flowing through them varies continuously 
while the diaphragm is in motion. 

This varying current circulates around the lower part 
of the iron core, d, and the two windings upon it form an 



24 



MODERN ELECTRICAL CONSTRUCTION. 



ordinary induction coil. Every variation of current strength 
in the circuit of the transmitter is by means of it reproduced 
in the circuit of the receiver, B, 

The essential parts of the telephone receiver are: The 
diaphragm /, very similar to that of the transmitter, the two 
magnets, g, and the electric circuit coming from the induction 
coil of the transmitter. T^e electric circuit, we have already 
seen, is traversed by electric currents exactly like those that 
flow in the circuit of the transmitter. These currents pass 
around electro-magnets, g, and attract the diaphragm, /, 
more or less strongly in proportion to the varying degrees of 
current strength. 

In this manner the diaphragm, /, of the receiver is made 
to vibrate in exact unison with that of the transmitter, and 
thus to reproduce exactly the sounds given to the trans- 
mitter. 

The transmitter is not absolutely necessary for the re- 




Figure 8 ' 

<^.eiver can be used as such, and in fact was so used at first. 
Lines of short distances can be operated without transmit- 
ters, but the speech will not be as plain. 



INDUCTION COIL. 



25 



Figure 8 is a diagram of the connections of two telephone 
instruments together with the necessary call bells. When the 
lines are not in use, the receivers, a, are hanging on the 
hooks, h, holding them down as shown by dotted lines. This 
leaves the circuit complete through the earth, g, magneto 
generator, e, bell /, line /, and duplicates of these parts at the 
right. When now the magneto generator is operated both 
bells will ring. When the receivers are removed, a spring 
forces the hook upwards making the connection shown in 
solid lines. This closes the battery circuit which must be 
open when the instrument is not in use or the battery wilJ 
run down. 

The talking circuit is now complete from earth, g, through 
the receiver, a, induction coil, b, line /, and duplicates of these 
parts at the right. 



The Induction Coil. 

Figure 9 is a diagramatic illustration of an induction 
coil as used mostly by medical men. Such an instrument 



It 


j/ 




H 


IL 1 ) f M 


Mf ff fJ[J 


4 








\f^ 










1 


m 




1 : 


m 


1 ' ;..- — - — 


ffiffllP^-^-- 


^y^ 








1 


^I'^TTTTTT 


^ 










\ 




u 


-< 


^ / 


\ 


6 © D <! 



Figure 9 

consists of an iron core, B, usually made up of a number 
of soft iron wires ; and two electrical circuits insulated from 
each other, and terminating in the two pair of binding posts, 
A and D. Of these two circuits A consists of a short length 



26 MODERN ELECTRICAL CONSTRUCTION. 

of comparatively heavy wire wound upon the iron core, and 
is known as the primary coil. D is a similar coil, but usually 
consisting of many more turns of wire, and the wire is also of 
much smaller gauge and is known as the secondary coil. 

The operation is as follows : A battery is connected to the 
binding posts, A, and current begins to flow in the circuit. In 
this circuit is an interrupter or vibrator, E, constructed 
similarly to the one described in connection with the electric 
bell. As current flows through the primary coil, it mag- 
netizes the core, B, and this attracts the armature, E, causing 
it to break the connection between itself and the adjusting 
screw. As this connection is broken, the current in A ceases 
to flow, the core is de-magnetized and the armature again 
connects with the adjusting screw. This action is repeated 
just as in the electric bell, and in consequence the core B, 
is rapidly magnetized and de-magnetized. 

Every time the core, B, is magnetized a current of electric- 
ity, lasting, however, only an instant, is induced in the second- 
ary coil, D. The magnetism in the core is caused by a cur- 
rent of electricity circulating around it, and currents of 
electricity are in turn produced by this magnetism in the 
other or secondary coil. 

This method of producing electric currents is known as 
electro-magnetic induction, and currents so produced are said 
to be ''induced" currents, hence the name induction coil. The 
currents so induced are alternating, that is, changing in 
direction. At the ''making" of the primary circuit, the cur- 
rent in the secondary coil is in a direction which opposes the 
magnetization of the core by the primary current ; at the time 
of "break" in the primary circuit, the induced current will be 
in the opposite direction. 

The tube, C, is movable and may be slipped entirely in over 
the iron core, or withdrawn entirely. If it is in, the currents 
which were before being induced in the secondary wires are 



BATTERIES 



27 



now induced in the metal of the tube and consequently the 
effect on the secondaries is very much reduced. 

The energy in the primary and secondary coils is always 
equal. If the two coils have the same number of turns, the 
currents and electro-motive forces are exactly alike. If the 
secondary coil has more turns of wire than the primary, 
the induced E. M. F. in it will be greater, but the current 
will be smaller and vice versa. The induction coil is very 
similar to the alternating current transformer, the main 
difference being that the transformer does not have an in- 
terrupter since the current supplied to it is itself constantly 
alternating. 



Batteries. 

Currents of electricity for commercial purposes are pro- 
duced either by dynamo electric machines or by batteries. 

A ''battery" is the name given to a number of cells con- 
nected together so as to produce a current greater than one 





Figure 10 Figure 11 

cell alone could produce. Figure 10 shows one cell of a kind 
that is generally used only intermittently, as for instance with 
door-bells. When the bell is not ringing the battery is idle. 



28 MODERN ELECTRICAL CONSTRUCTION. 

This style of cell is very useful for such work, but entirely 
useless for work requiring current continuously. The cell 
consists of a glass jar which is filled about J4 full of water 
in which a quantity of sal-ammoniac is dissolved. Immersed in 
this solution is a carbon cup or center, which forms the 
positive or + pole of the cell, and a zinc rod, carefully 
separated from the carbon by a rubber washer at the bottom 
and a porcelain tube at the top. So arranged, the current tends 
to flow, in the battery, from the zinc to the carbon and if the 
zinc and carbon outside of the cell be joined by a piece of 
wire or other conductor of electricity, the current will flow 
in the external circuit, from the carbon back to the zinc. If 
the zinc and carbon are not joined by a conductor of electric- 
ity there will be no current flow, but merely an electrical pres- 
sure tending to send a current. Each cell of this kind has 
an electro-motive force of about 1.4 volts. This is not suffic- 
ient for general use in connection with bells, etc., and in 
order to obtain greater current strength a number of cells 
are connected together in series as shown in Figure 11. 

This figure shows a different kind of cell, but will never- 
theless illustrate the method of connecting cells in series; 
which is, to connect the carbon or copper pole of the first 
cell to the zinc of the second, and again the carbon pole of the 
second to the zinc of the third, continuing in this way through 
all of the cells. Thus connected, all of the electro-motive 
forces act in one direction and if we have twelve cells each 
of an electro-motive force of 1.4 volts, we obtain a total 
electro-motive force to apply on our work of 12 X 1.4 or 16.8 
volts. 

Shoula we, however, connect six of the twelve cells as 
above, and then accidentally connect the other six in the 
opposite direction, that is, the zinc of the sixth cell to the 
zinc of the seventh, and then continue in this order, we should 
obtain no current whatever; six of our cells would tend to 



BATTERIES. 



29 



send current In one direction and six in the other, so that the 
result would be nothing. Should ten cells be properly con- 
nected to send current in one direction and two connected 
to oppose them, the net electro-motive force would be 10 X 1.4 
minus 2 X 1.4, which is 11.2. The ten cells would force current 
through the other two in the opposite direction. 

The electro-motive force of a cell is independent of its 
size, that is, a very small cell would set up just as high an 
electrical pressure as a very large one made of the same 
material. A large cell is, however, capable of delivering a 
much stronger current because its own resistance to the cur- 
rent flow is much less than that of a small cell. Large cells 
will, therefore, in most cases give very much better service 
than small ones. Especially in cases where considerable 
current is required as in electric gas-lighting and annunciator 
work, where it is always possible that two or three bells or 
fixtures may be called into action at the same time. 

In setting up and maintaining sal-ammoniac batteries, the 
following general rules should be observed: 

Use only as much sal-ammoniac as will readily be dis- 
solved; if any settles at the bottom it shows that too much 
has been used. Keep your battery in a cool place, but do 
not allow it to freeze. See that the jars are always about 
54 full of water. 

Keep the tops of glass jars covered with paraffir to 
prevent salts from creeping. 

The battery should never be allowed to remain in action 
(i. e., send current) continuously, or it will run down. If 
it has been run down through a short circuit or other cause, 
it should be left in open circuit for several hours; it will then 
usually ''pick up" again. 

The so-called dry-batteries are made up of about the 
same material, but applied in form of a paste. They are 



30 MODERN ELECTRICAL CONSTRUCTION. 

suitable for the same kind of work and especially handy for 
portable use. 

For continuous current work, such as telegraphy, for 
instance, the kind of battery shown in Figure 11 is generally 
used. The electro-motive. force of this style of battery is a 
little less than that of the sal-ammoniac battery and its re- 
sistance is considerably greater. 

Therefore, it is not well adapted for work requiring con- 
siderable current strength. Bells, telegraph instruments, etc., 
to be used with this battery require to be specially designed 
for it; the current being less in quantity must be made to 
circulate around the magnets many more times in order to 
fully magnetize them. 

The sal-ammoniac batteries cannot be used continually or 
they will run down; this battery must be kept at work always 
or it will deteriorate. 

This style of cell is known as the crow-foot or gravity 
cell, the action of gravity being depended upon to separate 
the essential elements of the solution. 

To set up this battery, the zinc crow-foot is suspended 
from the top of the glass jar as shown. The other element 
of the cell consists of copper strips riveted together and 
connected to a rubber-covered wire shown at the left of each 
cell, Figure 11. This copper is spread out on the bottom of 
the jar and clear water poured in until it covers the zinc. 
Next drop in small lumps of blue vitriol, about six or eight 
ounces to each cell. 

The resistance may be reduced and the battery be made 
immediately available hy drawing about half a pint of the 
upper solution from a battery already in use and pouring it 
into the jar; or, when this cannot be done, by putting into 
the liquid four or five ounces of pulverized sulphate of zinc. 

Blue vitriol should be dropped into the jar as it is con- 
sumed, care being taken that it goes to the bottom. The 



BATTERIES. 



31 



r. 



I 



^ 



need of the blue vitriol is shown by the fading of the blue 
color, which should be kept as high as the top of the copper, 
but should never reach the zinc. 

A battery of this kind when newly set up should be short 
circuited for a few hours, that is, a wire should be con- 
nected from the zinc at one end of the battery to the copper 
at the other. 

There are many styles of batteries and different chemicals 
are used with them. The two kinds above described are, 
however, the most used. The methods of connecting is in 
all batteries the same. 

Figure 12 shows a diagram of a battery connected in 

series ; the long thin lines repre- 
sent the copper or carbon pole 
from which the current flows in 
the external circuit and the short 
thick lines represent the zinc from 
which the current flows toward 
the copper inside of the cell. 
If we have a circuit of low resistance to work through 
and desire to increase the current, we may group our cells as 

shown in Figure 13, where two 
sets are in parallel. This arrange- 
ment will give a stronger current, 
but it is necessary to see that both 
groups of cells have the same 
electro-motive force; if they have 
not, the higher one will send the 
current through the lower. If the two batteries are not con- 
nected with similar poles together, they would be on short cir- 
cuit, and no current could be obtained in the external circuit. 



Figure 12 



r- r 


1 


■1 wm 




mm mm 




^ + V 


J 



Fi«rure 13 



CHAPTER III. 

Wiring Systems. 

There are numerous systems of electric light distribution. 
The oldest and the first to come into general use is shown 
diagramatically in Figure 14. This is the series arc system. 
In this system the same current passes through all of the 
lamps ; and as more or less lamps are required the E. M. F. 
of the dynamo must be correspondingly increased or dimin- 






y^ 7\ /\ /\ 



/\ /\ ?\ 7S. 7\ 7n 

Figure 14 

ished. This is accomplished by means of an automatic 
regulator connected to the dynamo. 

The current used with this system seldom exceeds ten 
amperes and large wires are never required. This system is 
best suited for street lighting where long distances are to be 
covered. 

In these diagrams, D represents the dynamo, and F, 
the ''field" coils of the dynamo. With constant current 
systems the ''fields" are usually in series with the armature 
of the dynamo, as shown in Fig. 14, and the lamps, so 
that the same current must pass through all. With constant 



WIRING SYSTEMS. 



33 



potential systems, the field coils are generally independent of 
the rest of the circuit. With such systems the current used 
in the circuit is so variable that it cannot be used in the 
fields. 

Another system, known as the multiple arc or parallel 
system, is shown in Figure 15. In this system the E. M. 
F. never varies, but the current is always proportional to the 








Q 



6 



6 



number of lights used. If, for instance, only one light is used, 
there is a current of about one-half ampere^ but if ten 16 
cp. lights are used there must be a current of about five 
amperes. Where many lights are used with this system, the 
main wires require to be quite large, and must always be 
proportional to the number of lights. This system is oper- 
ated usually at 110 volts and is suitable for residences, stores, 
factories and all indoor illumination. It is not well adapted 
to the transmission of light and power over long distances. 
The 3-wire system shown in Figure 16 combines many of 




U U U i i 



^Q 



t t t H t t t 



Figure 16 



the advantages of both the foregoing systems. As will be 
seen from the diagram, it consists of two dynamos connected 
in series and a system of wiring of one positive +, one nega- 
tive — and a neutral = wire. So long as an equal number of 



34 



MODERN ELECTRICAL CONSTRUCTION. 



lights are burning on both sides of the neutral wire, this 
wire carries no current, but should more lights be in use 
on one side of the system than on the other, the neutral wire 
will be called upon to carry the difference. If all the lights 
on one side are out, the dynamo on that side will be running 
idle. 

The currents in the neutral wire may be either positive 
or negative in direction. The principal advantage of this sys- 
tem is that with it double the voltage of the 2-wire systems 
is employed and yet the voltage at any lamp is no greater than 
with the use of two wires. It is customary to use 110 volts 
on each side of the neutral wire and this gives a total volt- 
age over the two outside wires of 220 volts. As the same 
current passes ordinarily through two lamps in series, we 
need, for a given number of lamps only half as much current 
as with 2-wire systems and can, therefore, use smaller 
wires. For the same number of lights and the same per- 







Figure 17 

centage of loss the amount of copper required in the two 
outside wires is only * one-fourth that of 2-wire systems; to 
this must be added a third wire of equal size for the neutral, 
so that the total amount of copper required with this system 
is ^ of that of 2-wire system using the same kind of lamps. 
Incandescent lamps are often run in multiple-series, as in 



WIRING SYSTE.MS. 



35 



Figure 17, without a neutral wire. The number of lamps to 
be used i:i series depends upon the voltage of the dynamo. 
If that is 550, live 110 volt lamps are required in each group, 
3r ten 55 volt lamps. 

If the filament of one lamp breaks all of the lamps in 



L . i_LL. I I iim 



'^^U^^ 



rO- 



-O 



' ^ u ^u 



o- 



Figure 18 

that group are extinguished and if one is to be used all must 
be used. 

Figure 18 shows the diagram of a senes-mwltiple system. 
This style of wiring should be avoided. 

A diagram of an alternating current system is shown in 



^ 



{ 





m 



Figure 19 

Figure 19. In this system extremely high voltage is used and 
consequently the currents are never very great. This makes 



36 MODERN ELECTRICAL CONSTRUCTION. 

it extremely useful for long distance transmission. Since, 
however, the high pressure employed cannot be used directly 
in our lamps it must be transformed into lower pressure. 
This is done by means of transformers, and it is possible to 
reduce the line voltage to any desirable extent. As the volt- 
age is reduced, however, the current increases and the wires 
taken from the transformers into the buildings must be as 
large as those for 2-wire systems using the same kind of 
lamps. The high pressure, or primary wires, are rarely 
allowed inside of buildings. 

The Transmission of Electrical Energy, 

We have seen that currents of electricity flow only in 
electrical conductors, and that these conductors are usually 
arranged in the form of wires. We have further seen that 
the power transmitted is proportional to the product of the 
volts and amperes used. The actual amount of energy trans- 
mitted being the product of the above multiplied by the time. 

Currents of electricity always encounter some resistance 
and in consequence of this resistance, generate heat : the 
generation of heat in any electric circuit being proportional 
to the square of the current multiplied by the resistance. 
This formula, P X R expresses the loss of electrical energy 
due to the* resistance of the conductors and which reappears 
in the form of heat. If this loss is not kept within reasonable 
limits, the wires will become very hot and destroy the in- 
sulation or ignite surrounding inflammable material. The 
above loss and hazard^ is generally guarded against by insur- 
ance companies and inspection boards by designation of the 
current in amperes which certain wires may be allowed to 
carry. 

Table No. 1 gives the currents which the National Board 
of Fire Underwriters has decided to consider safe and which 



ELECTRICAL TRANSMISSION 37 

should be closely followed, and on no account should wires 
smaller than those indicated be used. There is no harm and 
no objection to using wires larger than indicated, but neither 
is there much gained unless the run be a long one as we shall 
see further on. 

The table of carrying capacities shows a great discrepancy 
between the relative cross-section of large and small wires 
and the currents they are allowed to carry; thus a No. 0000 
wire has a cross-section about eight times as great as that of 
No. 6, yet is allowed to carry less than five times as much. 

This discrepancy arises from the different rate of heat 
radiation. The radiating surface or circumference of a small 
circle or wire is relatively to its cross-section much greater 
than that of a large circle, and other things being equal the 
ratio existing between the heat given to a body and its radiat- 
ing surface determine its temperature. 

We have seen before that the power (either for lights or 
motors) consists of two factors; current and pressure, ex- 
pressed respectively as amperes and volts. We have also seen 
that the power (watts) equals the product of these two; 
hence it follows, that as we increase either one, we may de- 
crease the other, or conversely, as one is decreased the other 
must be increased in order to deliver a given amount of 
power. We further know that it is the current alone which 
heats the wires and that accordingly as our currents are large 
or small, the wires used to transmit them must be large or 
small. It is obvious, therefore, that we can save much on 
copper by using higher voltages, since, if we double the 
voltage, we shall need only one-half as much current and can, 
therefore, use a much smaller wire. As an example : Sup- 
pose we have power to transmit which at 110 volts requires 
90 amperes. This requires a No. 2 wire containing 66,370 
circular mils. Now, if we double the voltage, we shall need 
only 45 amperes; this much we are allowed to transmit over 



38 MODERN ELECTRICAL CONSTRUCTION. 

a No. 6 wire which has only 26,250 circular mils. We must 
not, however, increase our voltage without due precaution and 
consideration, for high voltage is dangerous to life and in- 
creases the fire hazard. It also increases the liability to 
leakage and requires better and more expensive insulation 
which in a small measure offsets the other advantages. The 
usual voltage employed at present varies from 110 to 220 
volts for indoor lighting and power; 500 to 650 volts for 
street railway work and from 2 to 20,000 volts for long 
distance transmission. The higher voltages mentioned are 
seldom brought into buildings, and are nearly always used 
with some transforming device which reduces the pressure to 
110 or 220 volts for indoor lighting or power. 

The flow of current through a given lamp, motor, or re- 
sistance determines the light, power or heat obtainable from 
such device. We know that the flow of current in turn 
(other things being equal) varies as the E. M. F. maintained 
at the terminals of any of these devices. Consequently in 
order to obtain a steady flow of current it is necessary to 
provide a steady E. M. F. 

The loss of E. M. F. in any wire is equal to the current 
flowing in that wire multiplied by the resistance of the wire. 
Since it is impossible to obtain wires without resistance, it 
is also impossible to establish a circuit without loss and 
wherever electricity is used some loss must be reckoned with. 
We may make this loss as large or as small as we desire. 
Where the cost of fuel is high, it is important to keep this 
loss quite small, using for that purpose larger wires. On the 
other hand where ther^ is an abundance of cheap fuel, or, 
where, for instance, water power is used, it will be more 
economical to waste five or ten per cent of the electrical 
energy than to spend the money needed to provide the copper 
necessary to reduce the waste to one or two per cent. 

In this connection, however, it must not be overlooked that 



ELECTRICAL TRANSMISSION 39 

the quality of the service depends to a great extent upon the 
loss allowed and here the nature of the business supplied must 
be taken into consideration. In yards, warehouses, barns, 
etc., a variation of five or ten per cent in candle power may 
not matter much, but in residences or offices it is very 
annoying. 

The loss in voltage depends, as we have already seen, 
upon the current used, and the resistance of the wire em- 
ployed. If the current is decided upon, we can reduce the loss 
only by reducing the resistance; the resistance can be re- 
duced only by increasing the size of wire used. If we double 
the cross-section of the wire, we decrease the resistance one- 
half and consequently reduce the loss or variation in volt- 
age one-half. Thus it will be seen that as we attempt to 
reduce the loss in voltage to a minimum we shall require 
very large wires and thus greatly increase the cost of our 
installation. 

For instance, if a line be In operation with a loss ^f 
twenty per cent, by doubling the amount of copper, we reduce 
the loss to ten per cent. In order to reduce our loss to five 
per cent, we must again double the amount of copper; and 
to reduce the loss still more, say to 2^ per cent, a wire 
of double the cross-section of the last must be used. If the 
cost of copper in the original installation utilizing eighty per 
cent of the energy be taken as 1, then the cost of copper to 
utilize ninety per cent will be 2; of ninety-five per cent, 4; 
and of ninety-seven and one-half per cent, 8; and no amount 
of copper will ever be able to save the full 100 per cent. 
We must not overlook, however, that although a reduction of 
loss from four to two per cent requires us to double the 
amount of copper, it does not necessarily double the cost, of 
our installation, for In many cases it adds but a small per- 
centage to the total cost. For instance, if It were decided to 
use No. 12 instead of No. 14 wire in moulding or insulator 



40 MODERN ELECTRICAL CONSTRUCTION. 

work, the cost of labor would not be appreciably affected 
thereby; similarily in connection with a pole line, the dif- 
ference in total cost occasioned by the use of say No. 6 
instead of No. 10 wire would be smafl. 

' Calculation of Wires. 

In electrical calculations so far as they relate to wiring, 
the circular mil plays an important part, and it becomes 
necessary to thoroughly understand its meaning. The mil 
is the 1/1000 part of an inch, consequently one square inch 
contains 1,000x1,000 equals 1,000,000 square mils. If all elec- 
trical conductors were made in rectangular form, we should 
be able to get along nicely by the use of the square mil, but, 
since they are nearly all in circular form, the use of the square 
mil as a unit would, necessitate otherwise unnecessary figures. 
The circular mil means the cross-section of a circle one mil 
in diameter, whereas the square mil means a square each 
side of which is equal to one mil in length. Square mils, 
can, therefore, be transformed into circular mils by dividing 
by .7854, and circular mils into square mils by multiplying 
by .7854, since it fs well known that a circle which can be 
inscribed within a square bears to that square the ratio of 
.7854 to 1. 

To illustrate : Using square mils if we wish to determine 
the cross-section of a wire having a diameter of 50 mils, we 
must first square the diameter and then multiply by .7854; 
50 X 50 X .7854, or 1963.5, which is the cross section of the 
wire expressed in square mils. To express the cross-section 
in circular mils, we have but to square the diameter, or 50 X 
50 ^^ 2500 circular mils. The 2500 circular mils are exactly 
equal to the 1963.5 square mils. The adoption of the circular 
mil simply eliminates the figure .7854 from the calculations. 

The resistance of a copper wire having a cross-section of 



CALCULATION OF WIRES ^\ 

one mil and a length of one foot is from 10.7 to 10.8 ohms, 
vhe variation being due to the temperature of the wire. 10.8 
ohms is the resistance usually taken. This resistance in- 
creases directly as the length and decreases as the cross-sec- 
tion increases. The resistance of any copper wire can, there- 
fore, be found by multiplying its length by 10.8 and dividing 
by the number of circular mils it contains. Expressed in 

L X 10.8 

formula this becomes R = - ■ where L stands for the 

C. M. 
total length of wire in feet, and C. M. for the cross-section 
in circular mils, and R for the resistance in ohms. In 
order to find the loss in volts, we must multiply the resistance 
by the current used. Representing this current by I, the 
I X L X 10.8 

formula becomes ■ = V; V being the volts lost. 

C. M. 

It is, however, seldom necessary to find how many volts would 
be lost with a certain wire and current, but rather to find how 
many circular mils are necessary in a wire so that the volts lost 
may not exceed a certain percentage. In order to determine this, 
we transpose V and C. M. and the formula now becomes 
I X L X 10.8 

= C. M. This is the final formula and gives 

V 
directly the number of circular mils a wire must have so that 
the loss with this current and length of wire shall not exceed 
the limits set by V. 

As an example, we have a current of 20 amperes to trans- 
mit a distance of 200 feet and the loss shall not exceed 
two per cent; voltage 110. This requires 400 feet of wire 
(two wires 200 feet long) and two per cent of 110 is 2.2. We 
therefore have 20 X 400 X 10.8 divided by 2.2, which gives 
us 39,270 circular mils, which we see by table I is a little less 
than a No. 4 wire. 



42 . MODERN ELECTRICAL CONSTRUCTION. 

The above formula will answer for all 2-wire work» 
whether it be lights or power. 

It is simply necessary to find the current required with 
whatever devices are to be used. 

These calculations are not often made in actual practice. 
It is much easier to refer to tables such as II. Ill, IV, V, VI, 
given at the end of this volume, by which the proper size 
of wire can be determined at a glance almost. 

In connection with 3-wire systems using two lamps in 
series, we need to calculate the two outside wires only, the 
neutral wire should then be taken of the same size. We must 
however assume double the voltage existing on either side 
of the neutral; that is to say, a 2-wire system using 110 volts 
would be figured at 110 volts, while a 3-wire system, using 
110 volt lamps on each side of the neutral wire would be 
figured at 220 volts. 

It must also be noted that with 3-wire systems the cur- 
rent required is only >^ of that required with 2-wire sys- 
tems. Ordinarily we have two lamps in series and the same 
current passes through both. Applying this to our formula 
we see that with the 3-wire system the current I is only half 
as great as with 2-wire systems and (the percentage of loss 
in both cases being the same) V, which stands for the volts 
to be lost, becomes twice as great. Owing to these two fac- 
tors, the wire for 3-wire systems need have only % as many 
circular mils as that of a 2-wire system with the same per- 
centage of loss. To this must be added the neutral wire so 
that the total cost of wire must be Y^ of that for the 2-wire 
systems. 

The amount of copper required in power transmission for 
a given percentage of losB varies as the square of the voltage 
employed. By doubling the voltage we can transmit power 
with the same loss four times as far; or, if we do not change 
distance or wire, we shall have only one-fourth of the loss 



CALCULATION OF WIRES 43 

we had before. A practical idea of the laws governing the 
distribution of circuits and the losses in voltage and wire 
which are unavoidable may be gained from Figure 20. 

Figure 20 shows 96 incandescent lights arranged on one 
iloor and placed 10 feet apart each way. With all cutouts 
placed at A and circuits arranged as in No. 1, 2,080 feet of 
branch wiring for the eight circuits of 12 lights each, will be 
required. If the cutouts be placed in the center, B, the same 
length of wire will be necessary. We have in this case merely 
transferred the cross wires from one end of the hall to the 
center. If we arrange two sets of cutouts as at C and D 
•and run circuits as 3 and 4 the total amount of wire necessary 
will be only 1,920 feet. By this arrangement we avoid the 
necessity of crossing the space indicated by dotted lines at 
the right, opposite B. 

If we run the circuits on the plan of No. 2, the least amount 
of wire for the eight circuits will be 2,560 ft. Such wir- 
ing would require extra wires feeding the various groups. 
Should we run a set of mains along ACBD, and make 12 
circuits of the installation by placing one cutout for each 
eight lights, the amount of wire required will be 1,680 feet. 
If we run a set of mains through B as shown by dotted lines 
using 12 lights per circuit, 1,760 feet of wire will be re- 
quired. If we now double the number of lights in the same 
space or limit the number per circuit to six, we shall require 
3,200 feet of wire to feed them all from A, but only 2,400 to 
feed them from B; to feed them all from the two centers C 
and D will also require 2,400 feet. 

The most economical location of cutout centers will, with 
even distribution of light, and in regard to branch wiring 
only, be such that it is unnecessary to run circuits like No. 2; 
in other words, not more than the number of lights allowed on 
one circuit should lead away from it in one direction. 

Suppose, for instance, the number of lights be increased 



44 



MODERN ELECTRICAL CONSTRUCTION. 







\c 



iC 



'C 



5s5' 



o 



o o 



o 



oi n 



o 



/ • 



®. 



o^S( > "n 7f '°?f 



^-s^ 



5^^ 







nZHZDIZIZD 



n 



T) O 



OX I ^) () () ZZD 



O Q 



O 



®- 



n. 



( ) 



O U C3 O 



^C 



^c 



c 



Ic 



sd ^b 



•z 



o q 



c c 



R 



o 



o 



o 



qYi ^j c : 



Q 



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o o 



Figure 20 



CALCULATION OF WIRES 45 

by one-half or (which amounts to the same thing in wire), 
the number of lights per circuit be limited to eight. If we 
run all branch circuits from A, we shall need a total of 2,760 
feet. It will require just as much wire to run the 64 lights 
below X as was required to run the whole 96 before ; viz. : 
2,080 feet ; to this must be added the wire necessary to run the 
four circuits above which is 680 feet. By extending our 
mains to the point X, we can save eight runs of wire each 
equal in length to the distance between A and X. X is the 
point of extreme economy as regards branch wires and nothing 
can be gained in this respect by extending the mains any 
further unless several cutout centers are decided upon as 
before explained. Whether it be more economical to extend 
the mains to X, or run branch circuits from A, depends upon 
the relative cost, in this instance, of 30 feet of mains and 
480 feet of branch wires. 

With an uneven distribution of lights as indicated by the 
black circles, each of which may be taken as an arc lamp or 
cluster of incandescent lamps, the most economical location 
of cutouts will be at Z. To move them farther to the right 
would shorten the wires of five circuits and lengthen them on 
eight ; to move either up or down in the group of eight would 
also lenghten more wires than it would shorten. 

In laying out circuits for electric lights, however, we 
must not take into consideration the cost of wire only. In 
many cases the loss In voltage is of far greater importance, 
not only because it means a steady waste of power, but also 
because of unsatisfactory illumination, lamps in different 
parts of a circuit not being of the same candle power, or 
the light in one place varying greatly when lights in another 
place are turned on or off. 

Some idea of the variation in voltage in different parts 
of differently arranged circuits can be obtained from Figure 20. 
The length of wire in circuit 1 is 35 feet to the first lamp and 



46 MODERN ELECTRICAL CONSTRUCTION. 

10 feet from this to the next, etc. The voltage at the cut- 
out A is 110 and at each lamp is given the actual voltage 
existing at that point with all lamps burning. The wire of 
the circuit is No. 14 and with 55 watt lamps, the loss to the 
last lamp over a run of 145 feet is a trifle over two and one- 
half per cent when all lamps are burning. 

Circuit No. 2 is figured as of the same length as No. 1, 
and supplies the same number of lamps, but at a much greater 
loss, slightly over four per cent to the last lamp. Circuits 3 
and 4 feeding from C contain equal lengths of wire, but 
there is quite a difference in loss ; in 3 only .75 of one volt, 
while in 4 it is a little over two volts. From study of Figure 
20 we may learn that the arrangement of circuit 1 is fairly 
satisfactory especially if the nature of the work done under 
it is such that only part of the lamps are used at the same 
time. Circuit No. 2 is bad if all lights are used at once, and 
it should be wired with No. 10 or 12 wire. Whenever the loca- 
tion of lights is such as to allow a circuit like No. 3 to be run, 
the loss can be kept very low with a minimum of wire. In 
general the more cutout centers there are established in propor- 
tion to the number of lights, if mains are properly arranged, 
the less will be the loss in pressure and the more satisfactory 
the service. 



NOTICE.— DO NOT FAIL TO SEE WHETHER ANY 
RULE OR ORDINANCE OF YOUR CITY CONFLICTS 
WITH THESE RULES. 



Class A. 

STATIONS AND DYNAMO ROOMS. 

Includes Central Stations, Dynamo, Motor and Storage- 
Battery Rooms, Transformer Substations, Etc. 

L Generators. 

a. Must be located in a dry place. 

It is recommended that water-proof covers be provided, 
which may be used in case of emergency. 

Perfect insulation in electrical apparatus requires that the 
material used for insulation be kept dry. While in the con- 
struction of generators the greatest care is taken that ali 
current carrying parts are well insulated, still, if moisture is 
allowed to settle on the insulation, trouble is almost sure to 
occur. For this reason a generator should never be installed 
where it will be exposed to steam or damp air or in any place 
where through accident water may be .thrown against it. A 
location under steam or water pipes or close to an outside 
window should be avoided. 

b. Must never be placed in a room where any hazardous 
process is carried on, nor in places where they would be ex- 
posed to inflammable gases or flyings of combustible materials. 

In even the best constructed dynamos there is always more 
or less sparking at .the brushes and small pieces. of hot carbon 



48 MODERN KLECTKICAL CONSTRUCTION. 

are sometimes thrown off. As a general rule in buildings 
where there is considerable dust, such as in wood-working 
plants, grain elevators and the like, the dynamo is located in 
the engine room, which is generally isolated from the dusty 
part of the building. 

c. Must, when operating a1 a potential in excess of 550 
volts, have their base frames permanently and effectively 
grounded. 

Must, when operating at a potential of 550 volts or less, 
be thoroughly insulated from the ground wherever feasible. 
Wooden base frames used for this purpose, and wooden floors 
which are depended upon for insulation where, for any rea- 
son, it is necessary to omit the base-frames, must be kept 
filled to prevent absorp.tion of moisture, and must be kept 
clean and dry. 

Where frame insulation is impracticable, the Inspection 
Department having jurisdiction may, in writing, permit its 
omission, in which case the frame must be permanently and 
effectively grounded. 

A hig-h potential machine should be surrounded by an in- 
sulated platform. This may be made of wood, mounted on 
insulating- supports, and so arrangred that a man must always 
stand upon it in order to touch any part of the machine. 

In case of a machine having an insulated frame, if there is 
trouble from static electricity due to belt friction, it should 
be overcome by placing" near the belt a metallic comb connected 
with the earth, or by grounding- the frame through a resistance 
of not less than 300,000 ohms. 

The smaller generators are usually insulated on wooden 
base frames. A base frame suitable for this work is shown in 
Figure 21. Almost any kind of wood, well varnished, is very 
good for this purpose. The base frame is screwed to the floor 
or foundation and the slide rail (which is used where the 
dynamo is belted to the engine to allow the tightening and 
slackening of the belt) is independently attached to it, that is, 
the same bolt must not be used to hold the slide rail to the 
base frame and the base frame to the floor, as this would be 
liable to ground the frame. The direct connected machines 



GENERATORS. 



49 



(dynamo and engine on same bed plate) are often insulated 
by the use of mica washers and bushings surrounding the 
bolts which fasten the dynamo to the bed plate and by using 




Figure 21. 



Figure 22. 



an insulated flange coupling between the shaft of the dynamo 
and that of the engine. Figure 22 shows a section of a flange 
coupling insulated in this way, the heavily shaded parts rep- 
resenting the insulating material. 

The larger machines, which on account of their weight 
cannot be insulated, must be permanently and effectually 
grounded. Where the engine and dynamo are direct con- 
nected a very good ground is obtained through the engine con- 
nections. Where belts are used a good ground can be ob- 
tained by fastening a copper wire under one of the bolts on the 
dynamo and connecting the other end of the wire to available 
water pipes. In the case of high tension machines, especially 
series arc, the machine should always be surrounded by an 
insulated platform so arranged that a man must stand on it in 
order to touch any part of the machine, either live parts or 



50 



MODERN ELECTEICAL CONSTRUCTION. 



fraine, and in handling such a machine only one hand at a time 
should be used. A hardwood platform mounted on insulators 
will serve very well for this purpose or suitable platforms may 
be obtained from dealers in electrical supplies. 

Figure 23 shows a metallic comb such as is occasionally 
used to overcome the static electricity due to the friction of 
the belt. A strip of metal, one end of which is cut with a 




Figure 23. 



number of projecting points, is suspended crosswise a short 
distance above the belt. A wire connects this plate to any 
suitable ground. 

A resistance for grounding the generator frame in accord- 
ance with this rule is constructed of ground glass equipped 
with two metal terminals separated a short distance and con- 
nected by means of a lead pencil mark. One terminal is con- 
nected to the frame of the machine and the other to the ground. 

d. Constant potential generators, except alternating cur- 
rent machines and their exciters, must be protected from ex- 
cessive current by safety fuses or equivalent devices of ap- 
proved design. • 

For two-wire, direct-current generators, sing-le pole pro- 
tection will be considered as satisfying the above rule, pro- 



GENERATORS. 51 

vided the safety device is located in the lead not connected to 
the series winding. When supplying- three-wire systems, the 
generators should be so arranged that these protective de- 
vices will come in the outside leads. 

For three-wire, direct-current generators, a safety device 
must be placed in each armature, direct-current lead, or a 
double pole, double trip circuit breaker in each outside gen- 
erator lead and corresponding equalizer connection. 

In general, generators should preferably have no exposed 
live parts and the leads should be well insulated and thor- 
oughly protected against mechanical injury. This protection 
of the bare live parts against accidental contact would apply 
also to any exposed, uninsulated conductors outside the gen- 
erator and not on the switchboard unless their potential is 
practically that of the ground. 

Where the needs of the service make the above require- 
ments impracticable, the Inspection Department having juris- 
diction may, in writing, modify them. 

Constant potential generators are designed to carry a cer- 
tain amount of current without seriously overheating. If any 
considerable overload is put on a machine of this type a dan- 
gerous rise in the temperature of the generator and the wires 
connected to it will occur and a fire may result. To protect 
the apparatus some safety device must be installed in the main 
circuit which will cut off the current when it exceeds its 
normal maximum value. The safety fuse is commonly used 
for this purpose, but circuit breakers of approved design meet 
the requirements of the rule and may be used in place of the 
fuses. 

Alternating current generators are usually constructed in 
large units. If a safety device installed in the main circuit 
of one of these large machines should operate and open the 
circuit, the generating apparatus, dynamo and engine would 
momentarily be left in a dangerous condition owing to the 
fact of the load being suddenly removed from the generator. 

The sudden disrupting of the circuit of an alternating cur- 
rent generator gives rise to a momentary, excessive increase 
in the E. M. F., and as this is usually already very high 



52 



MODERN ELECTRICAL CONSTRUCTION. 



there is great tendency to pierce .the insulation of the genera 
tor winding. 

In view of these facts, and for the further reason that on 
short circuit the impedance of an alternating current arma- 
ture consisting of many coils in series is generally of such an 
amount as to limit the resultant current, alternating current 
generators are excepted from the general rule requiring pro- 
tection by safety devices. While the rule does not require 
protective devices in any alternating current generator, still 
it is the general practice, and it is advisable, .to provide fuses 
or circuit breakers on the smaller size generators such as are 
used in isolated plants for instance. 

Fuses are sometimes mounted on the generator itself, but 
the general practice at .the present time is to mount all fuses 
on the switchboard. For two-wire, direct current generators 



A 



OvV\ 
B 



Fiffure 24. 



one fuse will suffice, provided this fuse is located in the lead 
which is not connected to the series winding. The diagram 
Figure 24 shows the proper location of the fuses. An inspec- 
.tion of this diagram will also show the reason for this re- 
quirement. Two compound wound generators are shown con- 



GENERATORS. 



53 



nected in parallel. To avoid confusion the shunt field and 
switch connections are not shown. When the generators are 
operating together current from the brush on the right-hand 
side of machine A has two paths by means of which it can 
get to the positive bus bar. One of these paths is through its 
own series field and the other through the equalizer connection 
and series field of generator B. The current in the lead con- 
nected .to the series field may not be of as great strength as 
that generated in the armature ; or, due to the fact that it 
may be receiving additional current from the other machine 
through the equalizer connection, it may be of greater strength 
than that generated in the armature. A fuse placed in this 
lead could not, therefore, provide proper protection for the 
armature. 

Where a shunt wound generator is used the fuse may be 
placed in either lead. The same is true in the. case of a single, 
compound wound generator, for no equalizer connection is 
used in this case, and the current in both leads is always the 
same. 

Where generators are feeding a three-wire system the fuses 



-(3^ 



"CHaa 



/w(3 



aaJQ- 



Figure 25. 



should be placed in those leads which feed into the positive 
and negative mains. Figure 25. They should not be placed in 



i>4 MODERN ELECTRICAL CONSTRUCTION. 

the equalizer lead or in the lead connected to the series field 
for the reasons already given. It will be noticed that the 
two generators shown at the right of the diagram are con- 
nected in a reverse manner from those at the left. An ex- 
amination of the diagram, Figure 26, will show the reason for 



-Qh^ HO^aa 



Figure 26. 






this. In this case the placing of the fuse in the lead not 
affected by the equalizer current brings it in the lead con- 
nected to the neutral bus. If, with the fuse located in this 
line, the generator winding should become grounded a short 
circuit would result, as the neutral wire is always grounded, 
current flowing from the positive bus bar through the positive 
lead and the wires on the generator to the ground. The gen- 
erator would have absolutely no protection in a case of this 
kind and a fire would be sure to result. If the fuses were 
placed in the outside leads the circuits would be immediately 
opened and current shut off from the machine. 

Figures 27, 28 and 29 show the proper location of fuses 
in three-wire, direct current generator installations. In Fig- 
ure 27 is shown the wiring connection of a three-wire direct 
current generator. The armature of this generator contains 



GENEKATOBS. 



55 



two separate armature windings, each winding being provided 
with its own commutator, located on each side of the arma- 
ture. Two separate series field windings are provided, each 




Figure 27. 



field winding being connected in series with an armature wind- 
ing. The shunt field connections are not shown. 

To comply with the requirements each generator should 
be connected to the bus bars and fuses installed as shown. 
The simplified diagram, Figure 30, shows in a plainer manner 
the reason for this arrangement. Referring to the connections 
shown it will be seen that .the fuses protect each armature 
winding both from overload or from possible shorts caused 
by the grounding of the armature windings. A wrong ar- 
rangement of the fuses, and one that should be avoided, is 
shown in the diagram, Figure 31. In this case fuses are in- 
stalled in the lead from the series winding. The firs.t objec- 
tion to this arrangement is the one which has already been 
explained, /. e., the current from the armature having two 
paths open to it, one through the series field and one through 



56 



MODEUN ELECTKICAL CONSTRUCTION. 



the equalizer, .the armature could generate an excessive cur- 
rent without the fuse, which may be carrying only a part of 
the current, blowing. If for any reason one of the fuses 
shown did blow serious conditions might result owing to the 
' fact that the armature of that machine is still connected to the 
J armatures of all the remaining machines through the equalizer 
bus. A double-pole circuit breaker so arranged as to open 
both the series field lead and the equalizer lead would remove 
this objection, but, as the circuit breaker would be actuated 
by the current in the series field lead the objections before 





Fig-ure 28. 



stated still exist. Locating the fuse in the armature lead con- 
nected to the neutral bus would leave the generator unpro- 
tected in case of grounds. 

Figure 28 shows the*connections of the Westinghouse direct 
current, three-wire generator. In this generator direct cur- 
rent at the potential of the outside mains, usually 220 volts, 
is taken off the commutator side while the neutral connection 
is made through auto transformers to slip rings on the opposite 



GENEKATORS. 



67 



side of the armature shaft. Two separate series field windings 
are connected in series with each direct current armature lead. 
In order to place a fuse in each direct current armature lead, 
fuses would have to be mounted on the generator itself or the 
leads would have to be carried from the armature brushes to 
the switchboard and back to the series field. The usual pro- 
tection provided with this generator consists of double-pole, 
double-trip circuit breakers connected in the leads from the 
series fields and corresponding equalizer connection, this cir- 
cuit breaker being actuated by the current in the lead from 
the series field and arranged to open both series field and 
equalizer leads. As this generator is designed to withstand 
only a 25 per cent overload the circuit breakers should be 
interconnected so that in case one generator lead opens it 
automatically opens the remaining lead. 

Figure 29 shows the wiring connections of a compensator 




Figure 29. 

set. This set consists of two machines, the armature shafts of 
which are rigidly connected together. Each machine acts as 



58 MODEKN ELECTKICAL CONSTRUCTION. 

a motor or generator, depending on the condition of unbal- 
ance ; and they are used only to balance the system, other gen- 
erators supplying current to the outside mains. 

This class of apparatus is protected in the same manner 
as in the case just described. A double-pole, double-trip cir- 
cuit breaker should be installed in each outside lead and cor- 



Figure 30. Figure 31. 

responding equalizer lead. It might be well to state that with 
apparatus designed on the principle just described various 
details of construction of the machines, as built by the dif- 
ferent manufacturers, require a more complicated system of 
protection so that the above rule is not always exactly com- 
plied with. 

Circuit breakers, when used for protection in dynamo 
leads, are generally mounted on the switchboard and con- 
nected in the circuit ahead of the main switch. The circuit 
breaker as at present constructed is, in nearly all cases, a 
much more efficient and reliable device than the fuse, and its 
use is to be recommended. The fusing point of an ordinary 
fuse depends on the temperature of the fuse metal. When 
fuses are used in an engine room where the temperature is 
often very high the fuse may blow when it is carrying a cur- 
rent very much less than its rated capacity, and this will gen- 
erally result in a larger fuse being installed. The circuit 



GENERATORS. 59 

breaker is no.t affected by this increase in temperature. When 
a fnse blows from overload it generally occurs at a time when 
all the apparatus is in use and serious delays are apt to result 
before the fuse can be replaced. This objection does not exist 
where the circuit breaker is used. 

As to the relative currents at which the fuse and circuit 
breaker should be set to operate, authorities differ. Some ad- 
vise that both be set to operate at the same current strength 
so that the fuse, which takes a longer time to operate, will 
blow only in case the circuit breaker fails. Another recom- 
mends that the fuses be of such capacity as to carry any load 
which will be required of them and to set the circuit breaker 
a little higher than the fuses so that the fuses will operate on 
overload and the circuit breaker on short circuit. The prac- 
tice of setting the fuses at about 25 per cent above the circuit 
breaker seems to be preferred, for it frequently happens, when 
both are set to operate at the same current strength, the fuse 
alone will ''blow," due to the excessive heat produced in the 
fuse at full load. 

There is a tendency in the design of some of the newer 
generators to do away with binding posts, leads properly 
bushed through the generator frame and arranged for direct 
connection to leads from switchboard being provided instead. 
As this does away with exposed, live parts it is to be recom- 
mended. Where there are exposed live parts on the genera- 
tor or its connections they should be protected from accidental 
contact, except where they are at the same potential as the 
ground, as in the case of the neutrals on the direct current 
three-wire systems and the ground return on trolley systems. 

Cases are sometimes found where the cessation of current 
due to the blowing of a fuse could cause more damage than 
would result from an overload, as, for instance, where the 



60 MODERN ELECTRICAL CONSTRUCTION. 

dynamo operates some safety device. In cases of this kind the 
Inspection Department having jurisdiction may modify the 
requirements. 

e. Must each be provided w^ith a name-plate, giving the 
maker's name, the capacity in volts and amperes, and the 
normal speed in revolutions per minute. 

/. Terminal blocks when used on generators must be 
made of approved non-combu&tible, non-absorptive insulating 
material, such as slate, marble or porcelain. 

2. Conductors. 

From generators to sv^itchboards, rheostats or other instru- 
ments, and thence to outside lines. 

a. Must be in plain sight or readily accessible. 

Wires from generator to switchboard may, however, be 
placed in a conduit in the brick or cement pier on which the 
generator stands, provided that proper precautions are taken 
to protect them against moisture and to thoroughly insulate 
them from the pier. If lead-covered cable is used, no further 
protection will be required, but it should not be allowed to 
rest upon sharp edges which in time might cut into the lead 
sheath, especially if the cables were liable to vibration. A 
smooth runaway is desired. If iron conduit is provided, 
double braided rubber-covered wire (see No. 47) will be satis- 
factory. 

h. Must have an approved insulating covering as called 
for by rules in Class ''C" for similar work, except that in cen- 
tral stations, on exposed circuits, the wire which is used must 
have a heavy braided, non-combustible outer covering. 

Bus bars may be made of bare metal. 

Rubber insulations ignite easily and burn freely. Where 
a number of wires are brought close together, as is generally 
the case in dynamo rooms, especially about the switchboard, 
it is therefore necessary to surround this inflammable ma- 
terial with a tight, non-combustible outer cover. If this is 
not done, a fire once started at this point would spread 
rapidly along the wires, producing intense heat and a dense 
smoke. Where the wir^s have such a covering and are well 
insulated and supported, using only non-combustible materials, 
it is believed that no appreciable fire hazard exists, even with 
a large group of wires. 

Flame proofing should be stripped back on all cables a 
suflicient amount to give the necessary insulation distances 
for the voltage of the circuit on which the cable is used. The 
stripping back of the flame proofing is necessary on account 



CONDUCTORS. 61 

of the poor insulating- qualities of the flame proofing- material 
now available. Flame proofing may be omitted where satis- 
factory fire proofing is accomplished by other means, such as 
compartments, etc. 

c. Must be kept so rigidly in place that they cannot come 
in contact. 

d. Must in all other respects be installed with the same 
precautions as required by rules in Class "C" for wires carry- 
ing a current of the same volume and potential. 

e. In wiring switchboards, the ground detector, voltmeter, 
pilot lights and potential transformers must be connected to 
a circuit of not less than No. 14 B. & S. gage wire that is 
protected by an approved fuse, this circuit is not to carry over 
660 watts. 

For the protection of instruments and pilot lights on 
switchboards, approved N. E. Code Standard Enclosed Fuses 
are preferred, but approved enclosed fuses of other designs of 
not over two (2) amperes capacity may be used. 

Voltmeter switches having- concealed connections must be 
plainly marked, showing- connections made. 

A number of different methods are used for running wires 
in dynamo rooms. Where the dynamo is located in a room 
with a low ceiling, or where it is not desirable to run the 
wires open, metal conduits may be imbedded in the floor and 
the wires run in them. If the engine room is located in the 
basement or in any place where water or moisture is liable 
to gather in the conduits the wires should be lead covered. 
At outlets the conduits should be carried some distance above 
the floor level and close to the frame of the machine, where 
they will be protected from mechanical injury. If the space 
under the machine will allow it, the conduit should be ended 
there where it will be protected by the base frame. Where 
lead covered wires are used, the lead should be cut back some 
distance from the exposed part of the wire and the end of the 
lead should be* well taped and compounded so that no 
moisture can creep in between the lead and the insulation. 

In place of the metal conduits tile ducts can be used; or, 
if the floor is of cement, a channel may be left in the floor 



62 MODERN ELECTRICAL CONSTRUCTION. 

aiul the wires run into it. A removable iron cover should be 
I)rovided. 

The wires may be run open on knobs or cleats as described 
in Class C. Where there are many w^ires, cable racks, con- 
structed of wood or preferably iron, having cleats bolted to 
them, may be used. As a general rule moulding should not 
be used for this class of work. Especially in central stations 
the generators are often called upon for a very heavy overload 
and should the wires becomx overheated a fire is much more 
apt to result w^hen the leads are run in moulding than if they 
were run open where any trouble could be immediately no- 
ticed. 

3. Switchboards. 

a. Must be so placed as to reduce to a minimum the 
danger of communicating fire to adjacent combustible material. 

Special attention is called to the fact that switchboards 
should not be built down to the floor, nor up to the ceiling. 
A space of at least ten or twelve inches should be left between 
the floor and the board, except when the floor about the 
switchboard is of concrete or other fireproof construction, and 
a space of three feet, if possible, between the ceiling and 
the board, in order to prevent fire from communicating from 
the switchboard to the floor or ceiling, and also to prevent the 
forming of a partially concealed space very liable to be used 
for storage of rubbish and oily waste. 

b. Must be made of non-combustible material or of hard- 
wood in skeleton form, filled to prevent absorption of moisture. 

If wood is used all wires and all current-carrying parts of 
the apparatus on the switchboard must be separated therefrom 
by non-combustible, non-absorptive insulating material. 

c. Mus.t be accessible from all sides when the connections 
are on the back, but may be placed against a brick or stone 
wall when the wiring i§ entirely on the face. 

If the wiring is on the back, there should be a clear space 
of at least 18 inches between the wall and the apparatus on 
the board, and even if the wiring is entirely on the face it is 
much better to have the board set out from the wall. The 
space back of the board should not be closed in, except by 
grating or netting either at the sides, top or bottom, as sucii 
an enclosure is almost sure to be used as a closet for clothing 



SWITCHP-OARDS. 



63 



or for the storage of oil cans, rubbish, etc. An open space is 
much more likely to be kept clean, and is more convenient for 
making" repairs, examinations, etc. 

d. Must be kept free from moisture. 

e. On switchboards the distances between bare live parts 




Figure 32. 

of opposite polarity must be made as great as practicable, and 
must not be less than those given for tablet-boards (see No. 
53 A). 

The switchboard may be located in any suitable place in the 
dynamo room. It should generally be placed in a central 
position as close as possible, without inconvenience, to all 
machines and perfectly accessible. Do not locate a switch- 



64 MODERN ELECTRICAL CONSTRUCTION. 

hoard under or near a steam or water pipe or too close to 
windows, as these may accidentally he the means of wetting 
the board. 

The material generally used for the construction of switch- 
boards is slate or marble, free from metallic veins. If metallic 
veins are not guarded against they may cause great leakage 
of current, which will manifest itself in heating the slate or 
marble. 

The switchboard may be made of hardwood in skeleton 
form (see Figure 32), but in this case all switches, cutouts, 
instruments, etc., must be m.ounted on non-combustible, non- 
absorptive insulating bases, such as slate or marble and all 
wires must be properly bushed where they pass through the 
woodwork and must be supported on cleats or knobs. Wood 
base instruments are not approved. 

Marble or slate boards are usually set in angle iron frames 
and are much safer and better than the skeleton board shown. 
It is a good plan to have the iron legs rest on a wooden base, 
so that they will be insulated from the ground. 

Although only 18 inches clear space is required back of 
the board, where the board is back connected, this should be 
increased wherever possible, especially in the case of large 
boards. 

4. Resistance Boxes and Equalizers. 

(For construction rules, see N'o. 6o.) 

a. Must be placed on a switchboard or, if not thereon, 
at a distance of at least a foot from combustible material, or 
separated therefrom by a non-inflammable, non-absorptive 
insulating material such as slate or marble. 

This will require the use of a slab or panel of non-com- 
bustible, non-absorptive insulating material such as slate or 
marble, somewhat larg-er than the rheostat, which shall be 
secured in position independently of the rheostat supports. 
Bolts for supporting- the rheostat shall be ooimtersunk 
at least Vs inch below the surface at the back of the slab and 




RESISTANCE BOXES. 65 

'lied. For proper mechanical strength, slab should be of a 
thickness consistent with the size and weight of the rheostat, 
and in no case to be less than V2 inch. 

If resistance devices are installed in rooms where dust 
or combustible flyings would be liable to accumulate on them, 
they should be equipped with a dust-proof face plate. 

Ordinarily the dynamo field rheostat is mounted on the 
back of the board if the board is back connected, a small hand 
wheel being provided so that 
the rheostat may be operated 
from the front of the board. 
If the switchboard is in skele- 
ton form, or if the rheostat is 
placed on a wall, it should be 
mounted on a solid piece of 
slate or marble. Separate 
screws should be used for at- 
taching the rheostat to the slate Figure 33. 
or marble and the slate or marble to the wall, for, if the same 
screws were used for this purpose, they would be apt to ground 
the rheostat frame. (See Figure 33.) 

On central stations where current is furnished over a large 
area, there is on some of the circuits, especially the long ones, 
a considerable "drop," or loss of potential. In order to keep 
the voltage at the point of supply on these circuits at the 
proper value, the voltage at the station must be raised. This 
in turn causes the voltage on those circuits near the dynamo 
to become excessive. Equalizers, which are large resistance 
boxes generally constructed of iron wire or strips, and capable 
of carrying a heavy current, are connected in the circuits and 
adjusted at such resistances as to make the voltage at the 
various points of supply uniform. They are generally too 
heavy to mount on the board, but should be raised on non- 
combustible, non-absorptive insulating supports and should 
be separated from all inflammable material. 



66 MODERN ELECTRICAL CONSTRUCTION. 

b. Where protective resistances are necessary in connec- 
tion with automatic rheostats, incandescent lamps may be 
used, provided that they do not carry or control the main 
current or constitute the regulating resistance of the device. 

When so used, lamps must be mounted in porcelain recep- 
tacles upon non-combustible supports, and must be so arranged 
that they cannot have impressed upon them a voltage greater 
than that for which they are rated. They must in all cases be 
provided with a name-plate, which shall be permanently at- 
tached beside the porcelain receptacle or receptacles and 
stamped with the candle-power and voltage of the lamp or 
lamps to be used in each receptacle. 

c. Wherever insulated wire is used for connection be- 
tween resistances and the contact plate of a rheostat, the insu- 
lation must be slow burning (see No. 43). For large field 
rheostats and similar resistances, where the contact plates are 
not mounted upon them, the connecting wires may be run 
together in groups so arranged that the maximum difference 
of potential between any two wires in a group shall not exceed 
75 volts. Each group of wires must either be mounted on 
non-combustible, non-absorptive insulators giving at least ^2 
inch separation from surface wired over, or, where it is neces- 
sary to protect the wires from mechanical injury or moisture, 
be run in approved lined conduit or equivalent. 

5. Lightning Arresters. 

{For construction rules, see No. 63.) 

a. Must be attached to each wire of every overhead cir- 
cuit connected with the station. 

It is recommended to all electric lig"ht and power companies 
that arresters be connected at intervals over systems in such 
numbers and so located as to prevent ordinary discharg-es en- 
tering (over the wires) buildings connected to the lines. 

b. Must be located in readily accessible places away from 
combustible materials, and as near as practicable to the point 
where the wires enter the building. 

In all cases, kinks, coils and sharp bends in the wires be- 
tween the arresters and the outdoor lines must be avoided as 
far as possible. 

The switchboard does not necessarily afford the only loca- 
tion meeting thes^ requirements. In fact, if the arresters 



LIGHTNING ARRESTERS. 67 

can be located in a safe and accessible place av/ay from the 
board, this should be done, for in case the arrester should 
fail or be seriously damaged there would then be less chance 
of starting arcs on the board. 

c. Must be connected with a thoroughly good and perma- 
nent ground connection by metallic strips or wires having a 
conductivity not less than that of a No. 6 B. & S. gage copper 
wire, which must be run as nearly in a straight line as possible 
from the arresters to the ground connection. 

Ground wires for lightning arresters must not be attached 
to gas pipes within the buildings. 

It is often desirable to introduce a choke coil in circuit 
between the arresters and the dynamo. In no case should the 
g-round wires from the lightning- arresters be put into iron 
pipes, as these would tend to impede the discharge. 

d. All choke coils or other attachments, inherent to the 
lightning protection equipment, shall have an insulation from 
the ground or other conductors equal at least to the insulation 
demanded at other points of the circuit in the station. 

A lightning discharge is simply a discharge of electricity at 
very high potential. While the insulation of the ordinary wire 

serves very well for the voltages 
for which it is used it offers very 
little resistance to a current of 
such high potential, and providing 
the discharge can reach the ground 
\AAAAAAAAA/\/>/v/V by jumping through the insula- 
AAAAAAAAAAAAAA tion it will generally take that 

course unless some easier path is 
offered to it. A lightning arrester 
in its simplest form consists of 
Pig 34 two metal plates separated by a 

small air space as shown in Fig- 
ure 34. One of the plates is con- 
nected to the line and the other to the ground, a set being pro- 
vided for each line wire to be protected. 

The air space between the metal plates offers a much lower 



To 







Groon d 



68 MODEEN ELECTKICAL CONSTRUCTION. 

resistance to the passage of such a sudden current as a dis- 
charge of lightning consists of, than do the magnets of a 
dynamo, for instance, or highly insulated parts of the line. 
The current, therefore, jumps the air space and passes to 
ground. When the current jumps .this air space it produces 
an arc similar to that seen in an arc lamp, and after the light- 
ning discharge is over the dynamo current is very likely to 
maintain this arc and thus cause a short circuit from one 
lightning arrester through the ground to the other. Different 
methods of preventing this by interrupting the arc have been 
devised. 

Figure 35 shows the T. H. lightning arrester, in which 
the arc is extinguished by a magnetic field set up by the elec- 
tro-magnet. In the Wurts non-arcing lightning arrester (Fig- 
ure 36) the discharge takes place across the air gaps between 
the cylinders ; these are made of a metal which will not arc. 

A choice coil is simply a coil of wire, the size of wire and 
the number of turns depending upon the normal current and 
voltage of the system on which it is used. On 500 volt street 
railway circuits the choke coil sometimes consists of a spiral 
of five or six turns of heavy copper rod, while on high po- 
tential, alternating current circuits a greater number of turns 
and smaller wire is used. As every coil of wire has a certain 
amount of inductance, or, in other words, tends to hold back 
any change in the E. M. F., the placing of a coil in the cir- 
cuit between the lightning arrester and the apparatus on which 
the current is used affords a protection to the apparatus and 
forces the lightning discharge to pass to the ground through 
the lightning arrester. 

As the lightning arrester and choke coil are subjected to 
extremely high potentials they should be carefully insulated 
and properly located. 



TESTING. 



G9 



6. Care and Attendance. 

a, A competent man must be kept on duty where gen- 
erators are operating. 




Figure 35. 

b. Oily waste must be kept in approved metal cans and 
removed daily. 

Approved waste cans shall be made of metal, with legs 
raising can 3 inches from the floor and with self-closing 
covers. 

7. Testing of Insulation Resistance. 

a. All circuits except such as are permanently grounded 
in accordance with Rule 13 A must be provided with reliable 
ground detectors. Detectors which indicate continuously and 
give an instant and permanent indication of a ground are 
preferable. Ground wires from detectors must not be at- 
tached to gas pipes wnthin the building. 

b. Where continuously indicating detectors are not feasi- 



70 



MODERN ELECTRICAL CONSTRUCTION. 



ble the circuits should be tested at leas.t once per day, and 
preferably oftener. 

c. Data obtained from all tests must be preserved for ex- 



<9 



3k 



8> 



n ffn 11 tn o 



^S 



TTTl 




n — Es — m 



^ 



® t «8 



in — O — DT 



Ctound 



Figure 36. 

amination by the Inspection Department having jurisdiction. 
These rules on testing- to be applied to such places as may 
be designated by the Inspection Department having jurisdic- 
tion. 

The exceptions to this rule are 3-wire direct current sys- 
tems where the neutral is grounded and 2 and 3 v^ire alter- 
nating current secondaries v^^here the neutral or one side is 
grounded. 

Tn every installation of electric wiring there is a certain 
*'leak" of current. This leak is partly between the wires and 
the ground and between the wires themselves. The amount of 
leak varies, but is always dependent on the insulation resist- 



TESTING. 71 

ance. Where a small amount of wire is well installed the leak 
should be very small, but in the :ase of large installations 
or where the wiring has been poorly done the flow of current 
to ground or between the wires of opposite polarity may be- 
come quite large. Wires lying on pipes or on damp wood- 
work, crossed wires or live parts of apparatus mounted on 
wooden blocks, all tend to cut down the insulation resistance 
and increase the leak. The effects of poor insulation are : 
First, it represents a useless loss of current, and, second, and' 
more important, it means a possible cause of fire. 

The simplest way .to determine the insulation resistance of 
ci circuit is by means of a voltmeter. In Figure Zl if a volt- 
meter of known resistance is connected between one side of 
the circuit and the ground and there is a ground on the other 
side of the circuit, say at X, current will flow from the positive 
wire through the voltmeter, then through the ground at X to 
the negative side of the circuit. The voltmeter needle will 
indicate a certain reading which we will call V\ If the volt- 
meter is now connected directly across the circuit we get the 
circuit voltage, which we will call V. The two readings, V\ 
and V, are to each other as the resistance of the voltmeter 
is to the combined resistance of the voltmeter and the ground at 
X ; or, calling the resistance of the voltmeter R and the resist- 

\r R V-V^ 

ance of the ground at Xr, we get — = , orr = R . 

V R + r V' 

As an example : On a certain system the voltage across the 

mains is 110, while with the voltmeter connected as shown in 
Figure 37 we obtain a reading of 38. The resistance of the 
voltmeter is 10,500 ohms. 'Supplying the numbers in the for- 
110-30 

inula, r= 10,500 X = 28,000 ohms as the resistance to 

30 
ground the negative side of the system. If the voltmeter is 



72 



MODERN ELECTRICAL CONSTRUCTION. 



connected to ground from the other side, or — main, the resist- 
ance to ground of the + side can be obtained. 





AW 



Figure 37. 



Figure 38. 



If both sides of the system are grounded as at x and y, 
Figure 38, the voltmeter will be robbed of part of the current 
which would pass through it if Y were not in parallel with it. 
It will therefore not indicate correctly under such circum- 
stances. 

If, however, tests are frequently made and defects cleared 
up at once when noticed it will seldom happen that two 
grounds occur on the system at the 
same time. An engineer or dynamo 
tender will soon learn what the in- 
sulation resistance of .the plant in his 
charge should be and be governed ac- 
cordingly. 

A diagram of a direct current 
ground detector switch is shown in 
Figure 39. By throwing switch A 
down the — bus bar is connected to 
the ground through ^the voltmeter 
and by throwing switch B .the + bar 
is connected to ground through .the 
voltmeter. The ground wire should 
be run to a water or steam pipe • 

Fig. 39. 




MOTORS. 73 

(never to a gas pipe) or to some grounded part of the build- 
ing. If no good ground is obtainable one may be made as 
described under 13 A. 

8. Motors. 

The use of motors operating-, at a potential in excess of 
550 volts will only be approved when every practicable safe- 
guard has been provided. Plans for such installations should 
be submitted to the Inspection Department having: jurisdiction 
before any work is begun. 

a. Must, when operating at a patential in excess of 550 
volts, have no exposed live metal parts and have their base 
frames permanently and effectively grounded. 

Motors operating at a potential of 550 volts or less must 
be thoroughly insulated from the ground wherever feasible. 
Wooden base frames used for this purpose, and wooden floors, 
which are depended upon for insulation where, for any 
reason, it is necessary to omit the base frames, must be kept 
filled to prevent absorption of moisture, and must be kept 
clean and dry. Where frame insulation is impracticable, the 
Inspection Department having jurisdiction may, in writing, 
permit its omission, in which case the frame must be perma- 
nently and effectively grounded. 

A high-potential machine should be surrounded with an 
insulated platform. This may be made of wood, mounted on 
insulating- supports, and so arranged that a man must stand 
upon it in order to touch any part of the machine. 

In case of a machine having- an insulated frame, if there is 
trouble from static electricity due to belt friction, it should be 
overcome by placing- near the belt a metallic comb connected 
to the earth, or by grounding the frame through a resistance 
of not less than 300,000 ohms. 

Where motors with grounded frames are operated on sys- 
tems where one side is either purposely or accidentally 
grounded there exists a certain difference of potential between 
the windings and the motor frame , this difference of poten- 
tial depending on the part of the circuit considered. At some 
places in the winding it will be the full difference of po- 
tential at which the motor is operating and at other points 



74 MODERN ELECTRICAL CONSTRUCTION. 

practically nothing. Should the conductors accidentally come 
in contact or ''ground" on the motor frame a short circuit 
would result, as the circuit would then be completed through 
the motor frame and ground. To obviate this the motor frame 
should be insulated from the ground. This may be done either 
by setting the motor on a wood floor or by the use of a base 
frame, as with generators. A base frame should always be 
used where possible, for when a motor is set directly on the 
floor it is often impossible to keep the space under it clean, and 
there is always a liability of the floor being damp or of nails 
in the floor passing through the woodwork into some grounded 
part of the building or metal piping. A properly constructed 
base frame will allow of easy cleaning of the space under the 
motor. 

In the case of elevator or other motors where the shunt 
field is suddenly broken, a momentarily high voltage is induced 
in the field windings. If the frame of the motor is grounded 
this high voltage has a strong tendency to jump through the 
insulation of the wires to the metal work of the motor, thus 
grounding the circuit. 

h. Motors operating at a po.tential of 550 volts or less 
must be wired with the same precautions as required by rules 
in Class "C for wires carrying a current of the same volume. 

Motors operating at a potential between 550 and 3,500 
volts must be wired with approved multiple conductor, metal 
sheathed cable in approved unlined m^tal conduit firmly se- 
cured in place. The metal sheath must be permanently and 
effectively grounded, and the construction and installation of 
the conduit must conform to rules for interior conduits (see 
No. 25 and No. 49, a, f, and k), except that at outlets ap- 
proved outlet bushings shall be used. 

The motor leads or branch circuits must be designed to 
carry a current at least 25 per cent greater than that for which 
the motor is rated, in order to provide for the inevitable oc- 
casional overloading of the motor and the increased current 
required in starting, without overf using the wires; but where 



MOTORS. 75 

the wires under this rule would be overfused, in order to pro- 
vide for the starting- current, as in the case of many of the 
alternating- current motors, the wires must be of such size as 
to be properly protected by these larger fuses. 

The insulation of the several conductors for high potential 
motors, where leaving the metal sheath at outlets, must be 
thoroughly protected from moisture and mechanical injury. 
This may be accomplished by means of a pot head or some 
equivalent method. The conduit must be substantially bonded 
to the metal casings of all fittings and apparatus connected 
to the inside high tension circuit. It would be much preferable 
to make the conduit system continuous throughout by con- 
necting the conduit to fittings and motors by means of screw 
joints, and this construction is strongly recommended wher- 
ever practicable. 

High potential motors should preferably be so located 
that the amount of inside wiring- will be reduced to a mini- 
mum. 

Inspection Department having jurisdiction may permit the 
wire for high potential motors to be installed according to the 
general rules for high potential systems when the outside 
wires directly enter a motor room (see Section f). Under 
these conditions there would generally be but a few feet of 
wire inside the building and none outside the motor room. 

Good values to use for calculating the size of wire for 
branch conductors are given below. The question of loss of 
voltage is not taken into consideration here. 

110 volts 9.3 amperes per horsepower 

220 volts .4.6 amperes per horsepower 

500 volts 2 amperes per horsepower 

For mains supplying many motors it is not necessary to 
provide the twenty-five per cent, overload capacity, because it 
is not likely that all motors will start at the same time. If, 
however, any one motor has more than half the capacity of 
the whole installation, it is advisable to provide the overload 
capacity. For instance, if two motors, each of 50 amperes 
capacity, are fed over a line of 100 amperes capacity and 
one is started while the other is working at full load, they will 
overload that line twelve and one-half per cent. 

For mains supplying many small motors the size should 



76 MODERN ELECTRICAL CONSTRUCTION. 

be chosen for the total load connected, using the following 

values : 

110 volts 7.5 amperes per horsepower 

220 volts .*. .3.75 amperes per horsepower 

500 volts 1.65 amperes per horsepower 

Where there are a number of 110-volt motors installed on 
the Edison 3-wire system, providing the load is evenly balanced 
between the two sides, the mains may be figured as though 
the motors were operating at 220 volts. The reason for this 
will be easily seen when it is remembered that two 110-volt 
motors operating in series on 220 volts (as they do on the 
Edison 3-wire system) take only one-half the current they 
would if operated on a straight 2-wire 110-volt sys.tem. 

r. Each motor and resistance box must be protected by a 
cut-out and controlled by a switch (see No. 17a), said switch 
plainly indicating whether *'on" or "off." With motors of one- 
fourth horsepower or less, on circuits where the voltage does 
not exceed 300, No. 21 d must be complied with, and single 
pole switches may be used as allowed in No. 22 c. The switch 
and rheostat must be located within sight of the motor, except 
in cases where special permission to locate them elsewhere is 
given, in writing, by .the Inspection Department having juris- 
diction. 

The use of circuit-breakers with motors is recommended, 
and may be required by the Inspection Department having 
jurisdiction. 

Where the circuit-breaking device on the motor-starting 
rheostat disconnects all wires of the circuit, the switch called 
for in this section may be omitted. 

Overload-release devices on motor-starting- rheostats will 
not be considered to take the place of the cut-out required by 
this section if they are inoperative during the starting of the 
motor. 

The switch is necessary for entirely disconnecting the 
motor when not in use, and the cut-out to protect the motor 
from excessive currents due to accidents or careless handling 
when starting. An automatic circuit-breaker, disconnecting all 



MOTORS. 



77 



wires of the circuit may, liowever, serve as both switch and 
cut-out. 

In g-eneral, motors should preferably have no exposed live 
parts. 

For the larger size motors a cut-out must be installed for 
each motor, but with motors of ^ horsepower or less, where 




Figure 40. 

the voltage does not exceed 300, a cut-out need be installed 
for every 660 watts only. This allows about 5 ji horsepower 
motors, 3 Ye horsepower motors or 2 ^ horsepower motors 
on one cut-out. Every motor whether large or small must 
be controlled by a switch which will indicate whether the cur- 
rent is on or off. This is required to reduce the liability of a 
motor being accidentally left in circuit, which might result in 
serious trouble. Figure 40 shows a complete motor installa- 
tion as usually arranged. 

As a general rule fused knife switches are used for the 
larger motors, while with the rmaller motors cut-out blocks 



78 MODERN ELECTRICAL CONSTRUCTION. 

and indicating snap switches are often used. If the motor is 
y^ horsepower or less, and operated on a circuit where the 
vohage does not exceed 300, a single pole switch may be used. 
For all motors over ^ horsepower, and for all motors operated 
on voltages over 300, double pole switches nius.t be used. The 
object of locating the switch and starting box within sight 
of the motor is that, should any trouble occur when the motor 
is being started, such as a short circuit or overload, it will 
be immediately noticed and the current shut off. If the con- 
ditions are such that it is necessary to locate the motor out 
of sight of the switch and starting box the motor should be 
located in a safe place, away from inflammable material. A 
special permit should be obtained from the inspection depart- 
ment having jurisdiction in order that the exact conditions may 
be noted. 

d. Rheostats mus.t be so installed as to comply with all 
the requirements of No. 4. Auto starters must comply with 
requirements of No. 4 c. 

Starting: rheostats and auto starters, unless equipped with 
tig-ht casing's enclosing all current-carrying- parts, should be 
treated about the same as knife switches, and in all wet, dusty 
or linty places should be enclosed in dust-tig-ht, fireproof 
cabinets. If a special motor room is provided, the starting 
apparatus and safety devices should be included within it. 
Where there is any liability of short circuits across their 
exposed live parts being caused by accidental contacts, thej 
should either be enclosed in cabinets, or else a railing should 
bo erected around them to keep unauthorized persons away 
from their immediate vicinity. 

Auto starters answer the same purpose with alternating 
current motors that starting boxes do with direct current 
motors. Instead of an bhmic resistance an inductance is used 
to keep the current from attaining an excessive value while 
the motor is coming up to speed. 

In some cities .the local rules allow the starting box or 
rheos.tat to be mounted on asbestos board, in which case it 



MOTORS. 79 

must be mounted out from the wall on porcelairt knobs so that 
there will be at least one inch air space between the wall 
and the current-carrying parts. If the starting box or rheostat 
is .to be mounted on a wall or other support where the frame 
would be grounded, it may be attached to a wood support and 
the wood support then independently attached to the wall. 
The best construction is to use slate or marble. If slate or 
marble is used it must be a continuous piece which will entirely 
cover the space back of the rheostat and the frame of the 
rheostat should be screwed to the slate or marble and the 
slate or marble then independently screwed to the wall, never 
using the same screw for attaching both. 

A starting box is a device for limiting the current strength 
during the starting of the motor by inserting a resistance in 
series with the armature. The ohmic resistance of the arma- 
ture of a shunt or compound wound motor is ordinarily very 
small. When such a motor is at rest and the current thrown 
directly on, the full voltage is thrown across the small resist- 
ance of the armature. Consider for a moment the case of a 
1 horsepower 110 volt motor having an armature resistance of 
say 2 ohms, and taking, when running normally, 8 amperes. 
Suppose the current were thrown on without the use of a 
starting box. According to Ohm's law the current through 
the armature would be 110/2^55 amperes. The results, were 
55 amperes sent through the armature, can easily be imagined. 
Now, suppose a resistance of 8 ohms were inserted in series 
with the armature when starting. In this case 110/10=11 
amperes only would have to pass through the armature and 
this the armature can easily stand. As the motor begins to 
revolve a counter electro-motive force is generated which op- 
poses the inrush of current. This counter electro-motive force 



80 



MODERN ELECTRICAL CONSTRUCTION. 



increases until the motor reaches full speed and takes its nor- 
mal current. 

in .the example given above at the first step of the start- 
ing box there will be a current of 11 amperes flowing through 
a resistance of 8 ohms and the power consumed will be 
equal to I" R, or 968 watts^ which are lost in heat produced 
in the resistance wure. As this amounts to more than one 
horsepower thrown off in heat the advisability of mouat- 
ing the rheostat away from inflammable material and of prop- 
erly ventilating it can readily be seen. 

Figure 41 shows an illustration of an automatic starting 
box, and a diagram of the connections to a motor circuit. It 




AAAAA- 

^A/wvws 



O 



Figure 41. 

will be seen that the resistance coils are in series with the 
armature circuit. As the arm A is moved to the right, resist- 
ance is gradually cut out of the armature circuit until the 
arm reaches .the last point, where it is automatically held in 
position by means of the small magnet M, which is connected 



MOTORS. 



81 



in series with the field circuit. By tracing out the circuits it 
will be found that the field connection is made on the first 
point of the rheostat, so that when the arm A is in the ''ofY" 
position there is no current passing through the field coils. 




laaaaa- 



^VW\MA-| 

o- 



Figure 42. 

It will also be noticed that the last contact upon which the 
arm rests when ''ofY" is dead. If the supply current for any 
reason fails, current will cease .to flow around the coils of 
the magnet M and it will become demagnetized, thus allowing 
the arm A to fly back to the "off" position. This overcomes 
the possibility of the main current being momentarily shut off 
and then thrown on when all the resistance is out of the 
armature circuit. This device is known as "no-voltage" re- 
lease. 

Another device known as the "overload" release is shown 
in Figure 42, with a diagram of the connections. The wind- 
ing of the magnet M^ carries the main current. When the 
current exceeds a certain amount (which can be regulated 



82 



MODERN ELECTRICAL CONSTRUCTION. 



by a small nut) the armature below the magnet will be at- 
tracted, thus short circuiting the coil M and allowing the 
arm to fly back and shut off the current to the motor. This 
device cannot be considered to take the place of the regular 
cut-outs, as it is not operative during the starting of the 
motor. It can only operate after the arm A is held in posi- 
tion by the magnet M. 

Starting boxes are made in different designs to meet the 




Figure 43. 



requirements of the various classes of work on which they 
are used. Figure 43 shows a large automatic starting box 
where the resistance is cut out by the action of the solenoid 
S, which draws up the movable arm. When solenoids are 
used for this purpose it is often advisable to arrange the 



MOTORS. 



83 



connections so that when the movable arm has been raised 
to .the highest and last point a resistance, will be inserted 
in series with the solenoid to cut down the current and reduce 
the heating in the coil, as less current is required to hold 
the arm in place than to move it over the contacts. Incan- 
descent lamps are often used for this purpose and must be 
installed as in 4, Class A. 

A speed controller differs from a starting box mainly in 
the size of wire used as resistance. The resistance coils of a 




Figure 44. 



Starting box are wound with comparatively small wire con- 
nected in circuit for a short time only, generally from ten to 
twenty seconds, while in a speed controller the wire must be 
of sufficient size to carry the current as long as the motor 



84 



MODERN ELECTRICAL CONSTRUCTION. 



is running. Another difference between the starting box and 
speed controller is the automatic coil (Fig 41) M, which in 
the speed controller is arranged to hold .the arm A in any 
position in which it may be placed. This is accomplished in 
some types of speed controllers by a lever attached to an 
armature, which is attracted by the magnet M, the other end 
of the lever fitting into a series of indentations on lower part 
of movable arm. 

While the underwriters' rules do not require a speed con- 
troller to be automatic, still it is good practice to make them 
so, as the same principles apply to the starting of a motor with 
a speed controller as w^ith a starting box. 

Figure 44 shows a circuit breaker which is operative dur- 
ing the starting of the motor, and can be used to take the 
place of the switch required. 

As the arm of a starting box or speed controller is moved 
from one contact to another, more or less sparking results, 
and, as has already been stated, considerable heat is developed 
in the coils. A rheostat should never be located in a room 



mn 



t\A/V^ 



bvvvJ 



AAAA 



Figrure 45. 



where either inflammable gases or dust exist. If a starting 
box is to be located in a room where considerable dirt is 
apt to gather, or if the room is unusually damp, the starting 
box should be mounted in a dust-tight fire-proof box, which 



RIOTOKS. 85 

should be kept closed at all times, except when starting the 
motor. If the enclosing box is rather large, sufficient venti- 
lation of the coils will be obtained while the motor is being 
started and the door open. A speed controller should never 
be mounted in an enclosure unless the same is arranged to 
give a thorough ventilation to the outside air, as heat is con- 
stantly being generated in the coils of the rheostat, and this 
heat must be dissipated. A speed controller should never 
be located where dust or lint is apt to gather on it. If it 
is necessary to use one on a motor located in such a place, it 
should be mounted outside the room. 

In metal working establishments or in any place where 
there is a liability of the contacts on the switches or the 
starting boxes being short-circuited, they should be enclosed 
or suitably protected. 

e. Must not be run in series-multiple or multiple-series, 
except on constant-potential systems, and then only by special 
permission of the Inspection Department having jurisdiction. 

Figure 45 shows a series-multiple, and Figure 46 a multiple- 
series system of wiring. 

/. Must be covered with a waterproof cover when not in 





Fig-ure 46. 



use, and, if deemed necessary by the Inspection Department 
having jurisdiction, must be enclosed in an approved case. 
When it is necessary to locate a motor in the vicinity of 



86 MODEKN ELECTRICAL CONSTRUCTION. 

combustibles or in wet or very dusty or dirty places, it is 
generally advisable to enclose it as above. 

Such enclosures should be readily accessible, dust proof 
and sufficiently ventilated to prevent an excessive rise ot 
temperature. The sides should preferably be made largely of 
glass, so that the motor may be always plainly visible. This 
lessens the chance of its being neglected, and allows any 
derangement to be at once noticed. 

The usq of enclosed type motor is recommended in dusty 
places, being preferable to wooden boxing. 

From the nature of the question the decision as to details 
of construction must be left to the Inspection Department 
having jurisdiction to determine in each instance. 

Under certain conditions it is found necessary to enclose 
motors in dust-tight enclosures. The practice of building a 
small box which fits entirely around the motor, enclosing the 
pulley and provided with slots .through which the belt passes, 
is very unsatisfactory. While this construction prevents con- 
siderable dust from settling on and around the motor, still a 
great deal will be carried in by the belt. If the box is so 
made that it fits tightly around the shaft between the pulley 
and the motor frame and is otherwise well constructed, most 
of the dust and dirt can be kept out. As the efficient work- 
ing of the motor requires that it be kep.t as cool as possible, 
the box should afford sufficient ventilation. This may be 
obtained by making the box somewhat larger than the motor, 
thus allowing the heat to radiate from the sides, or the boxes 
should be ventilated to the outside air. 

A number of motors are so constructed that, by means of 
hand plates, they can be entirely enclosed. When they are so 
enclosed their efficiency and capacities are somewhat reduced, 
but cases are sometimes found w^here the conditions require 
motors of this kind to *be used. 

In places where there is considerable dust flying about in 
the air, and where the dust is not readily combustible, a fine 
gauze can be used to close the hand holes. This gauze will 
allow ventilation, bu.t will prevent the dirt from gathering 



MOTORS. 87 

inside the motor. The alternating induction motors, which 
are operated without brushes or collector rings, can be used 
in almost any location, as there is no sparking. 

g. Must, when combined with ceiling fans, be hung from 
insulated hooks, or else there must be an insulator interpo.sed 
between the motor and its support. 

Ceiling fans are generally provided with an insulating 
knob on which the fan hangs. If this is not provided, a sim- 
ple knob break can be used, or the fan can be suspended 
from a hook screwed into a hardwood block, provided the 
hook does not pass through the block into .the plaster, the 
block being separately supported from the ceiling. 

h. Must each be provided with a name-plate, giving the 
maker's name, the capacity in volts and amperes, and the nor- 
mal speed in revolutions per minute. 

i. Terminal blocks when used on motors must be made 
of approved non-combustible, non-absorptive insulating ma- 
terial such as slate, marble or porcelain. 

/. Variable speed motors, unless of special and appro- 
priate design, if controlled by means of field regulation, must 
be so arranged and connected that they cannot be started 
under weakened field. 

The speed of a motor may be changed either by inserting 
resistance in series with .the armature, thereby cutting down 
the voltage at the armature terminals; or by decreasing the 
field current through the addition of resistance in series with 
the shunt field winding. By this latter method the lines of 
force passing through the armature gap are considerably 
decreased and the armature must therefore revolve at a 
greater speed to develop the proper counter electro-motive 
force. When a motor is started under a weakened field, the 
starting torque being reduced, the armature is slow in coming 
up to speed. This prevents the rapid rise of counter E. M. 



88 



MODERN ELECTRICAL CONSTRUCTION. 



F. which takes place in the ordinary motor and consequent!}' 
the heavy rush of current through the armature is more likely 
to continue and burn out the armature. 

Unless motors are so designed that they do not require 
this excessive current when starting under a weakened field, 
the field rheostat, if separate from the starting rheostat, must 
be provided with a no-voltage release, such as is described 
in figure 41. When the field rheostat is combined with the 
starting rheostat the apparatus should be so constructed that 




Figure 47 

the motor cannot be started under a weakened field. Figure 
47 shows a starting rheostat of this kind, the last four con- 
tacts at the right being connected to the shunt field resistance. 
Moving the rheostat arm to the right cuts this resistance in 
series with the shunt field. 



9. Railway Power Plants. 

a. Each feed wire before it leaves the station must be 
equipped with an approved automatic circuit breaker (see No. 
52) or other device, which will immediately cut off the current 



TRANSFOKMERS. 



ill case of an accidental ground. This device must be mounted 
on a fireproof base, and in full view and reach of the attend- 
ant. 



10. Storage or Primary Batteries. 

a. When current for light or pov^er is taken from pri- 
mary or secondary batteries, the same general regulations 
must be observed as apply to similar apparatus fed from 
dynamo generators developing the same difference of poten- 
tial. 

b. Storage battery rooms must be thoroughly ventilated. 

c. Special attention is directed to the rules for wiring in 
rooms where acid fumes exist (see No. 24 i and ;). 

d. All secondary batteries must be mounted on non-ab- 
sorptive, non-combustible insulators, such as glass or thor- 
oughly vitrified and glazed porcelain. 

e. The use of any metal liable to corrosion must be 
avoided in cell connections of secondary batteries. 

Rubber-covered wire run on glass knobs should be used for 
wiring storage battery rooms. The knobs should be of such 
size as to keep the wire at least one inch from the surface 
wired over, and they should be separated 2^ inches for 
voltage up to 300 and 4 inches for voltage over 300. Water- 
proof sockets hung from stranded rubber covered wire and 
properly supported independently of the joints should be 
used ; these lights to be controlled by a switch placed out- 
side of battery room. All joints after being properly sold- 
ered and taped with both rubber and friction tape should be 
painted with some good insulating compound. This tends 
to keep all acid fumes away from the wire. 
* Acid fumes are not only liable to bring about a fire haz- 
ard, but are also irritating to employes. Thorough ventila- 
tion is therefore very important. 



90 MODERN ELECTiaCAL CONSTRUCTION. 

11. Transformers. 

(For construction ruleSj see No. 62.) 
(See also Xos. 13, ija, 36.) 

a. In central or sub-stations the transformers must be s^ 
placed that smoke from the burning out of the coils or the 
boiling over of the oil (where oil filled cases are used) could 
do no harm. 

If the insulation in a transformer breaks down, consid- 
erable heat is likely to be developed. This would cause a 
dense smoke, which might be mistaken for a fire and result in 
water beingr thrown into the building-, and a heavy loss there- 
by entailed. Moreover, with oil cooled transformers, especially 
if the cases are filled too full, the oil may become ignited and 
boil over, producing a very stubborn fire. 

b. In central or sub-stations casings of all transformer.' 

mus,t be permanently and effectively grounded. 

Transformers used exclusively to supply current to switch- 
board instruments need not be grounded, provided they are 
thoroughly insulated. 



NOTICE— DO NOT FAIL TO SEE WHETHER ANY 
RULE OR ORDINANCE OF YOUR CITY CON- 
FLICTS WITH THESE RULES. 



' Class B. 

OUTSIDE WORK. 

(Light, Power and Heat. For Signaling Systems, 
see Class E.) 

All Systems and Voltages. 
12. Wires. 

a. Line wires must have an approved weatherproof or 
rubber insulating covering (see No. 44 and No. 41). That 
portion of the service wires between the main cut-out and 
switch and the first support from the cut-out or switch on 
outside of the building must have an approved rubber insulat- 
ing covering (see No. 41), but from the above mentioned 
support to the line may have an approved weatherproof in- 
sulating covering (see No. 44), if kept free from awnings, 
swinging signs, shutters, etc. 

By service wires are meant those wires which enter the 
building. It is customxary to run the rubber-covered wire 
from the service switch and cut-out inside of building through 
the outer walls, and to leave but a few feet of wire to which 
'the line wires can later be spliced. This is illustrated in 
Figure 48, which shows how wires are run from pole to 
building. 

h. Must be so placed that moisture cannot form a cross 
connection between them, not less than a foot apart, and not 



92 



MODERN ELECTRICAL CONSTRUCTION. 



in contact with any substance other .than their insulating sup- 
ports. Wooden blocks to which insulators are attached must 
be covered over their entire surface with at least two coats 
of waterproof paint. 

c. Must be at least 7 feet above the highest point of flat 

roofs, and at least one foot above the ridge of pitched roofs 

over which they pass or to which they are attached. 

Roof structures are frequently found which are too low 
or much too lig-ht for the work, or which have been carelessly 
put up. A structure which is to hold the wires a proper 
distance above the roof in all kinds of weather must not only 
be of sufficient height, but must be substantially constructed 
Of strong material. 

It is well to avoid fastening wires perpendicular above one 
another, as in winter icicles may form which extend from the 




Se rv'ice 
Si kIcU 



Figure 48. 



top to the lower wire, apd the moisture on these will often 
cause much trouble. The rule requires that wires be 7 feet 
above flat roofs, and roof structures must, therefore, be made 
high enough to allow for "sag." In moderately long runs 
2 or 3 feet will be sufficient. For long runs, see following 



OUTSIDE WORK. 93 

table, taken from construction rules of Commonwealth Elec- 
tric Company of Chicago : 

The tension on wires should be such that the sag of a 
span of 125 feet will not exceed the amounts shown. 

Temperature, F...10 20 30 40 50 60 70 80 90 
Sag, inches 6 8 8 10 10 12 12 14 14 

This table will also be useful to consult when running 
wnres over housetops to which they are not attached, as it 
shows the variation in ''sag" due to different temperatures. 
Wires should be so run that even at the highest temperature 
they will still clear the buildings. Allowance should also 
be made for the gradual elongation of the wire to its own 
weight, giving way of supports or sleet that may at times 
weigh it down. 

d. Mus.t be protected by dead insulated guard irons or 
wires from possibility of contact with other conducting wires 
or substances to which the current may leak. Special pre- 
cautions of this kind must be taken where sharp angles occur, 
or w^here any wires might possibly come in contact with elec- 
tric light or power wires. 

Crosses, when unavoidable, should be made as nearly at 
right angles as possible. 

These guard wires are run parallel to and above the lower 
set of wires. Their object is to prevent the upper crossing 
wires, should they break, from coming in contact with the 
lower. A separate set of cross arms must be placed on the 
lower poles or above the lower wires to which the guard 
wires nrust be fastened. In Figure 49 1 and 2 show break 
insulators that may be used to electrically disconnect guard 
wires. 

e. Must be provided with petticoat insulators of glass or 
porcelain. Porcelain knobs or cleats and rubber hooks will 
not be approved. 

/. Must be so spliced or joined as to be both mechani- 



94 



MODERN ELECTRICAL CONSTRUCTION. 



cally and electrically secure without solder. The joints must 
then be soldered, to insure preservation, and covered with 
an insulation equal to that on the conductors. 

All joints must be soldered, unless made with some 
form of approved splicing device. This ruling- applies to joints 
and splices in all classes of wiring covered by these rules. 

Tn Figure 49 single and double petticoat insulators are 
shown. It is very often convenient to fasten such insulators 
upside down or horizontally, but this should never be done, 
as they will then fill with water or dirt and their insulating 
qualities be destroyed. 

g. Must, where they enter buildings, have drip loops out- 
side, and .the holes through wdiich the conductors pass must 
be bushed wnth non-combustible, non-absorptive insulating 
tubes slanting upward toward the inside. 

For low potential systems the service wires may be brought 
into buildings through a single iron conduit. The conduit to 
be curved downward at its outer end and carefully sealed 
or equipped with an approved service-head to prevent the 
entrance of moisture. The outer end must be at least one 













Figure 49. 



foot from any woodwoi*k and the inner end must extend to 
the service cut-out, and if a cabinet is required by the Code 
must enter the cabinet in a manner similar to that described 
in fine print note under No. 25 b. 

h. Electric light and power wires must not be placed on 
the same cross-arm with telegraph, telephone or similar wires, 
and when placed on the same pole with such w^ires the dis- 



OUTSIDE WORK. 95 

tance between the two inside pins of each cros5arm must not 
be less than twenty-six inches. 

i. The metalHc sheaths to cables must be permanently 
and effectively connected to ''earth." 

The telephone or telegraph wires are sometimes placed 
above the power wires, and it very often becomes necessary 
for a lineman to pass .through the lower wires to get at the 
upper. Great care is necessary to avoid coming in contact 
with high tension power wires while handling the telephone 
wires. 

Poles should not be set more than 125 feet apart; 100 or 
110 feet is good practice. For small wires poles with 6-inch 
tops are often used, but for heavier wires 7-inch .tops are 
advisable. The tops of pole should be pointed, so as to shed 
water, and the whole pole be well painted. Steps should be 
placed so that the distance between any two steps on the 
same side is not over 36 inches ; these steps should all, be the 
same distance apart, and should not extend nearer than 8 
feet to the ground. All *'gains" cut into poles should be 
painted before cross-arms are placed in them. Such places 
are more likely to hold moisture and rot than exposed parts. 
Wherever feed wires end or sharp angles occur, double cross- 
arms should be used, fastened on opposite sides of pole and 
bolted together. 

All bolts, lag screws, etc., should be galvanized. Poles 
should be set at least as far into the ground as shown in 
the following table: 

Length of pole. Depth in ground. 

35 feet 5j4 feet 

40 " 6 " 

45 " 6 " 



50 " 6y2 

55 *' 7 

60 " 8 



96 MODERN ELECTRICAL CONSTRUCTION. 

The holes should be large enough to admit of thorough 
tamping on all sides of bottom of hole. If the tamping at 
bottom of holt is not well done, the pole will always be shaky, 
no matter how much tamping may be done at the top. If 
the ground is soft, the pole may be set in cement, or short 
pieces of planking fastened to it at right angles underground. 
At the end of line or where sharp bends occur, strong gal- 
vanized guy cables fastened to poles six or eight feet long, 
buried underground, should be used. 

Trolley Wires. 

y. Must not be smaller than No. B. & S. gage copper 
or No. 4 B. & S. gage silicon bronze, and must readily 
stand the strain put upon them when in use. 

k. Mus.t have a double insulation from the ground. In 
wooden pole construction the pole will be considered as one 
insulation. 

/. Must be capable of being disconnected at the power 
plant, or of being divided into sections, so that, in case of 
fire on the railway route, the current may be shut off from 
the particular section and not interfere with the work of 
the firemen. This rule also applies to feeders. 

m. Must be safely protected against accidental contact 
where crossed by other conductors. 

Guard wires should be insulated from the ground and 
should be electrically disconnected in sections of not more 
than 300 feet in length. 

Ground Return Wires. 

n. For the diminution of electrolytic corrosion of under- 
ground metal work, ground return wires must be so arranged 
that the difference of potential between the grounded dynamo 
terminal and any point on the return circuit will not exceed 
twenty-five volts. 

It is sugg-ested that the positive pole of the dynamo be 
connected to the trolley line, and that whenever pipes or other 
underground metal work are found to be electrically positive 



OUTSIDE WORK. 97 

to the rails or surrounding earth, that they be connected by 
conductors arranged so as to prevent as far as possible cur- 
rent flow from the pipes into the ground. 

12 A. Constant-Potential Pole Lines, Over 5,000 Volts. 

(Overhead lines of this class unless properly arranged 
may increase the fire loss from the following causes : 

Accidental crosses between such lines and low-potential 
lines may allow the high-voltage current to enter buildings 
over a large section of adjoining country. Moreover, such 
high voltage lines, if carried close to buildings, hamper the 
work of firemen in case of fire in the building. The object 
of these rules is so to direct this class of construction that 
no increase in fire hazard will result, while at the same time 
care has been taken to avoid restrictions which would un- 
reasonably impede progress in electrical development. 

It is fully understood that it is impossible to frame rules 
which will cover all conceivable cases that may arise in con- 
struction work of such an extended and varied nature, and it 
is advised that the Inspection Department having jurisdiction 
be freely consulted as to any modification of the rules in par- 
ticular cases.) 
• 

a. Every reasonable precaution must be taken in arrang- 
ing routes so as to avoid exposure to contacts with other 
electric circuits. On existing lines, where there is a liability 
to contact, the route should be changed by mutual agree- 
ment between the parties in interest wherever possible. 

h. Such lines should not approach other pole lines nearer 
than a di^ance equal to the height of the taller pole line, 
and such lines should not be on the same poles with other 
wires, except that signaling wires used by the company 
operating the high-pressure system, and which do not enter 
property other than that owned or occupied by such com- 
pany, may be carried over the same poles. 

c. Where such lines must necessarily be carried nearer 
to other pole lines than is specified in Section h above, or 
where they must necessarily be carried on the same poles with 



98 



MODERN ELECTEICAL CONSTRUCTION, 



Other wires, extra precautions to reduce the liabiHty of a 
breakdown to a minimum must be taken, such as the use of 
wires of ample mechanical strength, widely spaced cross- 
arms, short spans, double or extra heavy cross-arms, extra 




Figure 50 

heavy pins, insulators, and poles thoroughly supported. If 
carried on the same poles with other wires, the high-pressure 
wires must be carried at least three feet above the other 
wires. 

d. Where such lines cross other lines, the poles of both 
lines must be of heavy and substantial construction. 

Wherever it is feasible, end-insulator guards should be 
placed on the cross-arms of the upper line. If the high-pres- 



OUTSIDE WORK. 99 

sure wires cross below iLo other lines, the wires of the 
upper line should be dead-ended at each end of the span to 
double-grooved, or to standard transposition insulators, and 
the line completed by loops. 

One of the following forms of construction must then be 
adopted : 

1. The height and length of the cross-over span may 
be made such that the shortest distance between 
the lower cross-arms of the upper line and any 
wire of the lower line will be greater than the 
length of the cross-over span, so that a wire break- 
ing near one of the upper pins would not be long 
enough to reach any wire of .the lower line. The 
high-pressure wires should preferably be above the 
other wires. 

By reference to Fig. SO it will be seen that the first plan 
of making cross-over is not very practical. In the lower left 
hand corner the vertical lines drawn alongside of the pole 
show the rate at which poles must be lengthened to comply 
with the rule when they are some distance from the pole 
to be crossed. 

If a line is to be crossed in this manner, economy and 
also good construction require that the poles be set close to the 
line to be crossed as shown at the right of the figure. The 
poles here are about twice the length of .the cross-arm apart. 
The wires between the tw^o poles cannot touch the lower 
wires and the expense of the cross-over is only the setting 
of one pole and its cross-arms, etc. With the poles se.t as 
close as this there remains, however, the possibility of a wire 
in one of the adjacent spans breaking and, if strongly whipped 
about by the wind, being lashed against the lower wires. 
Guard wnres can in a measure prevent such a wire coming 
in contact with the lower wire, but it is conceivable that the 
wire in question be broken off at such a distance from the 



100 



MODERN ELBCTRICA.L CONSTRUCTION. 



pole that it will swing over and lodge on top of the lower 
wires. If the cross-over poles are to be set farther apart to 
lessen this danger, .they must be increased two feet in height 
for every foot they are moved to one side. 

Figure 51 is a suggestion towards making crosses on a 
joint pole. It is simply a trough-like screen built around the 
lower wires and set so that it must catch the upper wires 
when they break and confine them so that the wind cannot 
whip them out. 

A cross-over made on a joint pole in some such manner 
as this is probably the most satisfactory. Wires are abso- 
lutely prevented from coming together, and such a pole 
being braced by the wires in two ways would seem to be 
quite safe. When wires cross at rather an acute angle the 




Figure 51 
screen mentioned stretched from pole to pole under the upper 
wires is probably the be^t safeguard. 

2. A joint pole may be erected at the crossing point, 
high-pressure wires being supported on this pole 
at least three feet above the other wires. Mechan- 
ical guards or supports must then be provided, so 
that in case of the breaking of any upper wire it 



OUTSIDE WORK. lOl 

will be impossible for it to come into contact with 
any of the lower wires. 

Such liability of contact may be prevented by 
the use of suspension wires, similar to those em- 
ployed for suspending- aerial telephone cables, 
which will prevent the high-pressure wires from 
falling in case they break. The suspension wires 
should be supported on high potential insulators, 
should have ample mechanical strength, and should 
be carried over the high-pressure wires for one span 
on each side of the joint pole, or where suspension 
wires are not desired guard wires may be carried 
above and below the lower wires for one span on 
each side of the joint pole, and so spread that a 
falling high-pre'ssure wire would be held out of 
contact with the lower wires. 

Such guard wires should be supported on hi.eh- 
potential Insulators or should be grounded, wiien 
grounded, they must be of such size, and so con- 
nected and earthed, that they can surely carry to 
ground any current which may be delivered by any 
of the high-pressure wires. Further, the construc- 
tion must be such that the guard wires will not 
be destroyed by any arcing at the point of contact 
likely to occur under the conditions existing. 

3. Whenever neither of the above methods is feasible 
a screen of wires should be interposed between 
the lines at the cross-over. This screen should be 
supported on high tension insulators or grounded 
and should be of such construction and strength 
as to prevent the upper wires from coming into 
contact with the lower ones. 

If the screen is grounded each wire of the screen 
must be of such size and so connected and earthed 
that it can surely carry to ground any current 
which may be delivered by any of the high pressure 
wires. Further, the construction must be such that 
the w^ires of screen will not be destroyed by any 
arcing at the point of contact likely to occur under 
the conditions existing. 

e. When it is necessary to carry such lines near buildings, 
they must be at such height and distance from the building 
as not to interfere with firemen in event of fire ; therefore, if 
within 25 feet of a building, they must be carried at a height 
not less than that of the front cornice, and the height must 
be greater than that of the cornice, as the wires come nearer 



102 



MODERN ELECTRICAL CONSTRUCTION. 



Wire 
building. 



to the building, in accordance with the following table 

Distance of wire Elevation of 

from building. above cornice of 

Feet. Feet. 

25 

20 2 

15 4 

10 6 

5 8 

2y2 9 

It is evident that where the roof of the building" continues 

nearly in line with the walls, as in mansard roofs, the height 



-Si 



a-^ — i 




Figure 52. 

and distance of the line must be reckoned from some part of 
the roof instead of from the cornice. 

A graphic illustration of the rule concerning the placing 
of poles near buildings is given in Figure 52. The upper 



TRANSFORMERS. 103 

group of figures and insulators shows the distance from the 
building and the corresponding height above high point of 
roof required with mansard roofs. Distance being measured 
from the roof. The lower. groups show measurements taken 
from cornice line as will be proper with ordinary flat roofed 
buildings. 

13. Transformers. 

(For construction rules, see No. 62.) 

(See also Nos. 11, 13A and 36.) 

Where transformers are to be connected to high-voltage 
circuits, it is necessary, in many cases, for best protection to 
life and property, that the secondary system be permanently 
grounded, and provision should be made for it when the trans- 
formers are built. 

a. Must not be placed inside of any building, excepting 
central stations and sub-stations, unless by special permission 
of the Inspection Department having jurisdiction. 

An outside location is always preferable; first, because it 
keeps the high-voltage primary wires entirely out of the 
building and, second, for the reasons given in the note to 
No. 11 a. 

b. Must no.t be attached to the outside walls of buildings, 
unless separated therefrom by substantial supports. 

It is recommended that the transformers be not attached 
to frame buildings when any other location is practicabl'e. 

As a rule transformers are fastened .to buildings on 
horizontal bars of wood. This method is as satisfactory as 
any if the wood itself is securely enough fastened to the 
wall. The wooden supports of the transformer should be 
fastened to the wall either by suitable expansion bolts or bet- 
ter still by bolts passing entirely through the wall. In fast- 
ening transformers to poorly constructed walls where per- 
mission to go through the wall cannot be obtained, some ad- 
vantage can be gained by supporting the transformer sticks 
set vertically as shown in Figure 53. It must be borne in 
mind .that there is not only a downward strain on the sup- 
ports but also an outward tipping strain. Almost any wall 



104 



MODERN ELECTRICAL CONSTRUCTION. 



will Stand the downward strain but in a loosely constructed 
wall there may not be a good hold for the bolts and a heavy 
transformer may tear them out as indicated. If the trans- 
former is supported as indicated the supports may be dis- 




Figure 53. 



tributed over a much larger wall area and a much greater 
leverage obtained against tipping strain than would be pos- 
sible with horizontally arranged timbers. 

The alternating current transformer consis.ts of an iron 
core upon which wires of two distinct electrical circuits are 
wound. One of these is known as the primary circuit, and in 
it the high pressure currents coming direct from the dynamo 
circulate. The other is known as the secondary circuit, and 
in it the low pressure currents used inside of building circu- 
late. These .two circuits are wound generally one over the 
other, and are very close together. The pressure used in the 
primary coil is from 1,000 to 5,000 volts, while in the secondary 
it is reduced usually to 110 or 220. 

It quite frequently happens that the insulation between the 



TRANSFORMERS. 



105 



two windings breaks down and thus the high pressure is acci- 
dentally brought into buildings. Under such circumstances 
should any one touch any live part of the installation while 
touching also grounded parts of the building death would very 
likely result. Also, should there be a weak spot in the insula- 
tion, it is quite likely the high pressure would pierce it at that 
point with a possible result of a fire. Many deaths and fires 



M l/S-2iO l 



m 



y U\,«r. 



Q} 



CS 



i50 I 







( - "\ r—- 


-) 


1 


1 II 






II II 




II 1 
















































































^ 


3 


3 


p/ 


/yfSe 230 


K. 



) c 



Figure 54. 



) c 



© 



200 r. 



have been caused in this way. If such lines are connected to 
ground the chances for harm are very much lessened, for the 
current will never take the path of high resistance through 
a man's body while a direct path through a low resistance 
wire is open to it. 

It must not be supposed that "grounding" one side of an 
electric light system is not often followed by serious conse- 
quences, for under such circumstances a ground coming on any 
other part of the system will cause a short circuit at once. 



1C6 MODERN ELECTRICAL CONSTRUCTION.' 

The grounding in these cases is to be looked upon as the 
lesser of two evils rather than as an advantage. With al- 
ternating currents, the chances of possible damage from 
grounding are much less than with direct currents, because 
earh transformer with its small group of lamps is a system 
by itself and nat affected by grounds on other transformers. 
Thus a 5,000 light alternating current installation would con- 
sist of from 25 to 50 separate systems, each independent of 
defects on the rest, while in a continuous current installation 
a ground on the most remote branch circuit would in con- 
junction with a ground on the opposite pole of any other part 
of the system form a short circuit. 

Methods of grounding secondary wires of alternating cur- 
rent transformers are shown in Figure 54, taken fiom an 
instruction book issued by the Commonwealth Electric Com- 
pany of Chicago. 

In connection with 3-wire systems, grounding of the cen- 
tral wire can do little harm, because ordinarily the neutral 
wire seldom carries much current, and that current is apt to 
vary in direction so .that the electrolytic effect will be on the 
whole quite negligible. 

There is, of course, the hazard brought about by the fact 
that a ground coming on one of the outside wires will imme- 
diately form a short-circuit in connection with the ground 
on the neutral. 

In connection with 3-wire systems, however, it is of the 
greatest importance (as more fully explained further on) that 
the neutral wire remain intact, and it being thoroughly 
grounded at all available outside places will help to keep it so. 

13 A. Grounding Low-Potential Circuits. 

The groiindingr of low-potential circuits under the follow- 
ing regulations is only allowed when such circuits are so 



GROUNDING. 107 

arranged that under normal conditions of service there will 
be no passage of current over the ground wire. 

Direct-Current 3-Wire System. 

a. Neutral wire may be grounded, and when grounded 
the following rules must be complied with : — 

1. Must be grounded at the Central Station on a metal 

plate buried in coke beneath permanent moisture 
level, and also through all available underground 
water and gas-pipe systems. 

2. In underground systems the neutral wire mus.t also 

be grounded at each distributing box through the 
box. 

3. In overhead systems the neutral wire must be 

grounded every 500 feet, as provided in Sections 
c to g. 

Inspection Departments having jurisdiction may require 
grounding if they deem it necessary. 

Two-wire direct-current systems having no accessible neu- 
tral point are not to be grounded. 

Alternating-Current Secondary Systems. 

h. Transformer secondaries of dis.tributing systems should 
preferably be grounded, and when grounded, the following 
rules must be complied with : — 

1. The grounding must be made at the neutral point, or 

wire, whenever a neutral point or wire is accessible. 

2. When no neutral point or wire is accessible, one side 

of the secondary circuit may be grounded, pro- 
vided the maximum difference of potential between 
the grounded point and any other point in the cir- 
cuit does not exceed 250 volts. 

3. The ground connection must be at the transformer 

or on the individual service as provided in sec- 
tions c to g, and when transformers feed systems 
with a neutral wire the neutral wire must also be 
grounded at least every 250 feet for overhead sys- 
tems and every 500 feet fpr underground systems. 



108 MODERN ELECTRICAL CONSTRUCTION. 

Inspection Departments having- jurisdiction may require 
grrounding if they deem it necessary. 

Ground Connections. 

c. When the ground connection is inside of any building, 
or .the ground wire is inside of or attached to any building 
(except Central or Sub-stations) the ground wire must be 
of copper and have an approved rubber insulating covering 
National Electrical Code Standard, for from to 600 volts. 
(See No. 41.) 

d. The ground wire in direct-current 3-wire systems must 
not at Central Stations be smaller than the neutral wire 
and not smaller than No. 4 B. & S. gage elsewhere. The 
ground wire in alternating current systems must never be less 
than No. 4 B. & S. gage. 

On three-phase system, the ground w^ire must have a 
carrying capacity equal to tliat of any one of the three mains. 

e. The ground wire should, except for Central Stations 
and transformer sub-stations, be kept outside of buildings as 
far as practicable, but may be directly attached to the build- 
ing or pole by cleats or straps or on porcelain knobs. Staples 
must never be used. The wire must be carried in as nearly 
a straight line as practicable, avoiding kinks, coils and sharp 
bends, and must be protected when exposed to mechanical 
injury. 

This protection can be secured by use of an approved 
moulding, and as a rule the ground wire on the outside of a 
building should be in moulding at all places where it is 
witliin seven feet from the ground. 

/. The ground connection for Central Stations, transform- 
er sub-stations, and banks of transformers must be made 
through metal plates buried in coke below permanent moisture 
level, and connection should also be made to all available 
underground piping systems including the lead shea.th of un- 
derground cables. 

g. For individual transformers and building services the 
ground connection may be made as in Section /, or may be 
made to water piping systems running into the build- 
ings. This connection may be made by carrying the ground 



GROUND PLATES. 109 

wire into the cellar and connecting on the street side of 
meters, main cocks, etc. 

Where it is necessary to run the ground wire through any 
part of a building it shall be protected by approved porcelain 
bushings through walls or partitions and shall be run in 
approved moulding, except that in basements it may be sup- 
ported on porcelain. 

In connecting- a ground wire to a piping" system, the wire 
should be sweated into a lug- attached to an approved clamp, 
and the clamp firmly bolted to the water pipe after all ruot 
and scale have been removed; or be soldered into a brass plug 
and the plug forcibly screwed into a pipe-fitting-, or, where 
the pipes are cast iron, into a hole tapped into the pipe itself. 
For larg-e stations, where connecting to underground pipes 
with bell and spigot joints, it is well to connect to several 
leng-thg, as the pipe joints may be of rather high resistance. 

Where ground plates are used, a No. 16 Stubbs' gage 
copper plate, about three by six feet in size, with about two 
feet of crushed coke or charcoal, about pea size, both under 
and over it, would make a ground of sufficient capacity for a 
moderate-sized station, and would probably answer for the 
ordinary substation or bank of transformers. For a larg^e 
central station, a plate with considerably more area mig-ht 
be necessary, depending upon the other underground con- 
nections available. The ground wire should be riveted to 
the plate in a number of places, and soldered for its whole 
leng-th. Perhaps even better than a copper plate is a cast- 
iron plate with projecting forks, the idea of the fork being 
to distribute the connection to the ground over a fairly ])road 
area, and to g-ive a large surface contact. The ground wire 
can probably best be connected to such a cast-iron plate by 
soldering- it into brass plug-s screwed into holes tapped in the 
plate. In all cases, the joint between the plate and the g-round 
wire should be thoroughly protected against corrosion by 
painting it with waterproof paint or some equivalent. 



NOTE.— DO NOT FAIL TO SEE WHETHER ANY 
RULE OR ORDINANCE OF YOUR CITY CONFLICTS 
WITH THESE RULES. 



Class C. 

INSIDE WORK. 

(Light, Power and Heat. For Signaling Systems, 
see Class E.) 

All Systems and Voltages. 

GENERAL RULES. 

14. Wires. 

(For special rules, see A'os. id, i8, 24, 33, 38 and 39.) 

a. Must not be of smaller size than No. 14 B. & S. gage, 
except as allowed under Nos. 24 7' and 4S b. 

The exceptions being wires used inside of fixtures and 
flexible cord ased to suspend individual electric lights. For 
general purposes a wire smaller than No. 14 is too easily 
broken, either through a sharp kink or by drawing too tight 
with tie wires. To avoid trouble from kinks or sharp bends, 
wires smaller than 14 should preferably be stranded. 

b. Tie wires must have an insulation equal to that of the 
conductors they confine. 

The use of some form of confining- knob or insulator which 
will dispense with tie wires is recommended. 

This is considered necessary, because very often the tie 
wire cuts through the insulation of the wire it confines, and if 
the tie wire should come in contact with other than its msu- 



INSIDE WORK. 



Ill 



lating support, there would still be good insulation. Tn Figu-e 
55, (1) and (2) illustrate the method of tying usually em- 
ployed with small wires on insulators; (4) shows a method 





1 i-ii \ *- ! r— Ti 

Vse screws for split Knohs 

and cleats. 





Figure 55. 



employed with larger wires. This is also especially useful, 
because slack can be taken up if the tie wire is arranged to 
draw the main wire about half way around the insulator; (6) 



112 



MODERN ELECTRICAL CONSTRUCTION. 




Figure £^ 



INSIDE WORK. 113 

^hows a4:not tied into the wire, as is usual where the end of 
the wire connects into cut-outs or switches. At (5) insula- 
tors are arranged to hold large wires. It is not advisable to 
tie large wires to insulators, as .the weight of the wire will 
soon cause it to cut through the insulation. Cleats, such as 
shown at (8) and (9), are preferable. 

c. Must be so spliced or joined as to be both mechanically 
and electrically secure without solder. The joints must then 
be soldered to insure preservation, and covered with an insu- 
lation equal to that on the conductors. 

Stranded wires must be soldered before being fastened 
under clamps or binding screws, and whether stranded or 
solid when they have a conductivity greater than that of No. 
8 B. & S. gage they must be soldered into lugs for all terminal 
connections. 

All joints must be soldered unless made with some form 
of approved splicing device. This ruling applies to joints and 
splices in all classes of wiring covered by these rules. 

On the left at the upper part of Fig. 56 is shown the well- 
known Western Union joint. Before joining wires they should 
be thoroughly cleaned by scraping wi.th the back of a knife or 
sand or emery paper. The insulation should be removed, as 
indicated at ^ ; if it is cut into as at a, it is very likely that 
the wire will be "nicked" and will be likely to break at that 
point. It is also more difficult .to tape a joint properly if the 
rubber has been cut in this way than it is with the rubber cut 
as at b. After the joint has been made it is covered with 
soldering fluid, a formula for which is given below. In lieu 
of this there are soldering sticks and salts, already prepared, 
9n the market. 

The following formula for soldering fluid is suggested : — 

Saturated solution of zinc chloride 5 parts 

Alcohol 4 parts 

Glycerine ^ 1 part 

The joint having been thoroughly covered with one of 



114 MODEEN ELECTRICAL CONSTRUCTION. 

these preparations is next heated with a gasoline or alcohol 
torch and a small piece of solder allowed to melt on it near 
the center. It is well to avoid heating too much at the ends 
of the joint, as it weakens the wire. After the joint is partly 
cooled wipe off all moisture and cover with layers of rnhber 
tape, enough, at least, so that it is equal in thickness lo the 
rubber insulation on the wire used, as shown at a and b. If 
the rubber tape is put on before the wire has entirely cooled 
the remaining heat will assist in vulcanizing the rubber. This 
rubber tape is then covered with friction tape to keep it in 
place. Before taping joints the outer braid of the wire should 
be carefully skinned back. If any of the cotton threads of 
which it consists were to be left in contact with the bare wire, 
they would, when moist, form a leak, which might prove trou- 
blesome. If joints are exposed to the weather it will be well 
to paint them over with some insulating paint to keep rhe 
friction tape in place, as it will otherwise soon work loose 
when it becomes dry. 

At c and d ''tap" joints are shown. The method shown 
at d is preferable, because .the wire cannot easily work loose. 
The method of joining shown at e is useful when, for instance, 
two wires, each of which is fastened to an insulator, are to be 
joined. The wares can be drawn very tight in this way. 
This sort of joint is very common in fixture work, and should 
be finished off as at f. 

Twin wares other than flexible cord are allowed only in 
metal conduits, and joints in them should be made only within 
the junction boxes. When joints in conduit are unavoidable, 
twin wires should be joined as at g, so that the joints are not 
opposite each other. Joints in flexible cord should be avoided 
as much as possible. 

In splicing stranded wires it is customary to remove some 
of .the center strands to avoid making a very bulky splice. All 



INSIDE WORK. 115 

Stranded wires must Idc soldered where fastened under binding 
screws; this refers also to flexible cord used in sockets. The 
best way to solder the ends of cords is to dip them in melted 
solder; a blow torch will easily overheat small v/ires and 
leave them brittle. 

Figure 57 shows lead covered wire spliced and laped. In 
handling lead covered wire great care must be exercised 
(especially with paper insulated) that it be not bruised and the 
lead not punctured. The lead covering is of use only as a 
protection against water ; if it admits the least bit of moisture 
it is worse than useless. The ends of lead covered wires 
should always be kept sealed until ready for use; in damp 
places the paper insulation may absorb moisture, which will 
ground the wire on .the lead. When installed the ends should 
always be sealed against moisture. Lead covered wires should 
never be used where there is a liability of nails being driven 
into them. 

Joints in lead covered wires are made just as in ordinary 
wires. Extreme care is necessarv that no moisture be left on 




Fig'ure 57. 

the wire when it is taped or covered up. Before the wire is 
joined a sleeve (Figure 57) is slipped over one of the wires. 
Af.ter the joint has been made and taped, this sleeve is placed 
so as to cover it, and the ends split and arranged to fit close 
against the lead on the wires. That part of the lead which 
mus.t be soldered to make the joint watertight is scraped until 
it is perfectly bright and then coated with tallow candle grease. 
It can then be soldered with an iron, or melted solder can be 



116 



MODEKN ELECTRICAL CONSTRUCTION. 



poured on it and wiped around it, as plumbers do. If a 
soldering iron is used it must not be too hot and not allowed 
to remain in one place too long, as the lead itself melts at 
nearly the same temperature as the solder. An inexperienced 
workman may burn more holes into the lead than he close?. 
If a neat job is desired, that part of the lead which is to be kept 
free of solder is covered with lampblack and glue, or ordinary 
paper hanger's paste, or a mixture of flour and water boiled, 
so as to prevent the solder from taking on it. 

d. Must be separated from contact with walls, floors, 
timbers or partitions through which they may pass by non- 
combustible, non-absorptive insulating tubes, such as glass or 
porcelain, except as provided in No. 24 ii. 

Bushing-s must be long- enough to bush the entire length 
of the hole in one continuous piece or else the hole must 




loom 



\> 




Figure 58. 

first be bushed by a continuous waterproof tube. This tube 
may be a conductor, such as iron pipe, but in that case an 
insulating bushing must be pushed into each end of it ex- 
tendmg far enough to keep the wire absolutely out of contact 
with the pipe. 

The exception mentioned is in regard to wires at outlets 



INSIDE WOKK. 



117 



where they are required to be in approved flexible tubing from 
the last insulator to at least one inch beyond plaster, or end 
of the cap on gas piping. This is shown in Figure 58. The 
reasons for the separation of wires from everything but their 
insulating supports are many. Should a bare live wire come 
in contact with damp woodw^ork or masonry, there would 
very likely be some flow of current to ground and through the 
ground to the other pole of the dynamo or other wire. This 
flow of current may gradually char the woodwork, and in 
time start a fire; or it may gradually eat away the wire, finally 
causing it to break. When a wire is eaten away, as shown 
at c and e, Figure 59, if it is carrying much current, the thin 




Figure 59. 



part w^ill become very hot and will set fire to whatever inflam- 
mable material may be near it- If the current flow to the 
ground continues, the positive wire will finally be entirely 
severed, and an arc, similar to that noticed in an ordinary arc 
lamp, will be established, and will continue until the wire has 
been burned away and the space between the two ends becomes 



118 MODERN ELEK:tRICAL CONSTRUCTION. 

too great for the arc to maintain itself. The negative wire, 
to which the current flows, is not eaten away in this manner, 
and such current flow is only possible when two wires of a 
system are in electrical connection with the ground. This 
action may, however, occur, even if the two grounded wires 
are miles apart. Wires and gas pipes are oft-en destroyed 
through intermittent contact ; for instance, if a wire makes a 
good contact to a gas pipe and there is a small leak to the pipe 
no particular harm will be done as long as the contact remains 
good. Should, however, the contact be intermittent, there will 
be a small arc at each break, and this will, little by little, burn 
holes into the gas pipe and into the wire. This action will 
take place on either a positive or negative wire. Non-com- 
bustible supports for wires are further useful in that they 
tend to prevent flames from the rubber insulation (which is 
very easily ignited from any of the above causes) from spread- 
ing to surrounding material. 

Figure 59 consists of copies of specimens showing effects 
of electrolysis, short circuits, and heating of lamp. These 
illustrations are copied from fire reports of the National Board 
of Underwriters. 

At a is shown a piece of gas pipe, which had been subject 
to electrolytic action until finally a hole had been eaten 
through the metal ; ^ is a socket which had been short cir- 
cuited, and the excessive damage was due to overfusing of 
circuit. 

At c and e, the effects of electrolysis on wire are shown ; 
r is a piece of underwriter's wire (not approved in moulding), 
which had been used in damp moulding, the leak to ground 
through the dampness causing the gradual eating away of the 
wire ; c shows a breakdown in the insulation and subsequent 
electrolytic action on the wire, causing it finally to break. 
This wire had been used in a roundhouse, where the sulphur 



INSIDE WOKK. 



119 



fumes and the condensation of escaping steam on insulators 
had formed a path to ground. At d is an incandescent lamp 
which had been covered with a towel, the confined heat soft- 
ening the glass and setting fire to the towel. The danger of 
fire from overheated lamps is much greater than is generally 
supposed. Small lam.ps and lamps subject to a little excess 
of voltage are especially dangerous, and many instances are 
on record where they have charred woodwork and set fire 
to cloth or paper shades. 

It may in many cases seem unnecessary to have bushings 
in one piece long enough to pass through a floor, or wide 
wall ; but especially in passing through floors, it is very easily 
possible for wires to become crossed between the joists; that 




Figure 60. 



Figure 61. 



Figure 62, 



is, the wire entering at the right above the floor may be 
brought out at the left below the floor and the other wire 
through the opposite holes. In such a case the two wires of 
opposite polarity will be in contact, and should the insulation 
give out from any cause whatever, such as abrasion, or the 
gnawing of rats and mice, there would be nothing to prevent 
a short circuit and consequent fire. In passing through floors 



120 MODEKN ELECTiaCAL CONSTIIUCTION. 

or walls the wires often come in contact with concealed pipes 
or other grounded material, so that only by making the bush- 
ings continuous can the wires be properly protected. 

Figure 61 shows short bushings arranged in iron pipe. 
Figure 62 shows a case where there is an offset in the wall. 
Cases of this kind very often occur. Sometimes the floor can 
be taken up and an iron conduit, properly bent, put in place ; 
the wires being reinforced with flexible tubing; or the wires 
placed on insulators. In this latter case the floor must not be 
put down until the inspector has examined the wires. The 
wires may be run on top of the floor to such a place where 
a continuous bushing may be dropped through the floor. The 
wires on top of the floor must be then protected by a suitable 
boxing of at least the same dimensions as given for boxing 
on side walls. 

e. Must be kept free from contact with gas, water or other 
metallic piping, or any other conductors or conducting ma- 
terial which they may cross, by some continuous and firmly 
fixed non-conductor, creating a permanent separation. Devia- 
tions from this rule may sometimes be allowed by special per- 
mission. 

Where one wire crosses another wire the best and usual 
means of separating them is by a porcelain tube on one of the 
wires. The tubing must be prevented from moving out of 
place either by a cleat or knob on each end, or by taping It 
securely in place. 

The same method may be adopted w^here wires pass close 
to iron pipes, beams, etc., or, where the wires are above the 
pipes, as is generally the case, ample protection can frequently 
be secured by supporting the wires well with a porcelain cleat 
placed as nearly above the pipe as possible. 

This rule must not he construed as in any way modifying No. 
24, Sections h and j. * 

Figure 63 is a sectional view of the manner in which wires 
arc usually run through joists in bushings. For small wires 
bushings should preferably be installed as shown at top; never 
as shown in the middle row. For larger wires the holes must 



INSIDE WORK. 121 

be bored as straight as possible ; otherwise it will be difficult 
to pull wires through. The quantity of wire needed is also 




Figure 63. 

somewhat increased by slanting the holes. In open places 
wires are generally installed on insulators as shown in Fig- 
ure 64. 

Figure 64 shows different methods employed where one 
wire crosses another. The method at the left, which is more 
suited to large stiff wires, does not quite comply with the rule, 
but is very often used. The other two methods are preferable. 
Insulating supports should always be provided at the place 
of crossing to prevent the upper wires from sagging and 
resting on the lower; also to prevent any strain from coming 
on tap joints. Approved flexible tubing such as circular loom 
is also often used in crossing wires and pipes. In dry loca- 
tions it is quite safe and does not break as easily as .tubes, 
but should never be used where there is any likelihood of 
dampness. 

/. Must be so placed in wet places that an air space will 
be left between conductors and pipes in crossing, and the 
former must be run in such a way that they cannot come in 
contact wi.th the pipe accidentall)^ Wires should be run over 
rather than under pipes upon which moisture is likely to 
gather or which, by leaking, might cav.se trouble on a circuit. 

This is a rule that is very often violated, as much work is 
done using loom, as shown at the left of Figure 65, and is 
quite safe with gas pipes. With cold water pipes, which are 



122 



MODERN ELECTKICAL CONSTRUCTION. 



likely to sweat, or with steam pipes, it is very bad practice. 
Where pipes are close against a ceiling it is better either to 
fish over them or drop wires some distance below them as 
illustrated at the right of the figure. No part of the wiring 
should be in contact with pipes. On side walls where ver- 




Figure 64. 



tical wires run across horizontal pipes the only safeguard 
would be to box the pipes and run the moisture to one side. 
The most harm is done by water on the insulators. If these 
can be kept dry it does not matter much about wires which 

Figure 65. 

hang free in the air. Whatever form of insulation is used 
in crossing pipes, it must be continuous. Short bushings 
strung on the wire, where a large pipe or number of pipes 
are being crossed, is not satisfactory, as the bushings are 



INSIDE WOKK. 123 

apt to separate or moisture gather in the space between them. 
The insulation must also be firmly attached to the wires. If 
knobs are not used as shown in Figure 64 to keep the bush- 
ings in place, they must be taped to the wire. 

g. The installation of electrical conductors in wooden 
moulding or where supported on insulators in elevator shafts 
will not be approved, but conductors may be installed in such 
shafts if encased in approved metal conduits. 

Wires supported on insulators in such places are very likely 
to be disturbed, especially in freight elevators. Moulding is 
often so impregnated with oil and the draft in an elevator 
shaft is usually so strong that a blaze once started would 
quickly run to the top. 

15. Underground Conductors. 

a. Must be protected against moisture and mechanical 
injury where brought into a building, and all combustible 
material must be kept from the immediate vicinity. 

b. . Must not be so arranged as to shunt the current 
through a building around any catch-box. 

By reference to Figure 66 the meaning of this rule will 
be made clear. With wires run as show^n it would be easy 
for any one having disconnected one service switch to believe 
all wires in the building dead, while they were in reality still 
being kept alive by the other switch. This connection would 
allows current to pass from one street main to another without 
going through the fuses in the street catch-box. 

c. Wliere underground service enters building through 
tubes, the tubes shall be tightly closed at outlets with asphalt- 
um or other non-conductor, to prevent gases from entering 
the building through such channels. 

d. No underground service from a subway to a building 
shall supply more than one building except by written permis- 
sion from the Inspection Department having jurisdiction. 



124 



MUDEKN ELECTIUCAL CONSTKUCTION. 



16. Table of Carrying Capacity of Wires. 

{Sec tables in back of book.) 

17. Switches, Cut-Outs, Circuit-Breakers, Etc. 

(For construction rules see Nos. 51, 52 and 53.) 

a. On constant potential circuits, all service switches and 
all switches controlling circuits supplying current to motors 
or heating devices, and all cut-outs, unless otherwise provided 
(for exceptions as to switches see Nos. 8r and 21a; for ex- 
ceptions as to cut-outs see No. 21 a and b) must be so arranged 
that the cut-outs will protect and the opening of the switch 
or circuit-breaker will disconnect all of the wires; that is, in 
the two-wire svstem the two wires, and the three-wire system 



1 



AllStrcctMains 
FusedHere 




^-^^^SS;^^^^^^^^^^^:^^\\^^^ ^ 



5TP^EE:TMAl^4^ 



Figure 66. 



the three wires, must be protected by the cut-out and discon- 
nected by the operation*of the switch or circuit-breaker. 

This, of course, does not apply to the grounded circuit of 
street railway systems. 

The exceptions arc in regard to motors of 54 H. P. or 
less on circuits of not over 300 voUs and incandescent cir- 



INSIDE WORK. 



125 



cults of not over 660 watts where single pole switches are 
allowed. Fiirtlur explanation of the exceptions will he given 
in connection with the rules mentioned ; 21 a and h, and 22 c. 
In connecting double-pole snap sw^itches the w^ireman 
should be very careful. Most of these switches cross polari- 
ties as shown in Figure 67, and if connected wrong will form 
short circuits. Many of them have been connected that way, 
even by wnremen of some experience. 

h. Must not be placed in the immediate vicinity of easily 
ignitable stuff or where exposed to inflammable gases or dust 
or to flyings of combustible material. 

When the occupancy of a building is such that switches, 
cut-outs, etc., cannot be located so as not to be exposed to 
dust or flyings of combustible material they must be enclosed 
in approved dust-proof cabinets with self-closing doors, ex- 
cept oil swatches and circuit breakers which have dust-tight 
castings. 

Whenever an electric current is broken, whether by fuse or 
sw'itch, an arc varying with the current strength is formed. 





Figure 67. 



Figure 68. 



Figuro ()). 



Should a switch be only partly opened, this arc will continue 
and consume the metal of the sw^itch until the gap in which it 
burns becomes too long, when the current will be broken. 



126 MODERN ELECTRICAL CONSTRUCTION. 

Meanwhile there is much heat generated which may readily 
communicate to inflammable materia, near by. 

There seems to be no reason except economy of wire why 
cut-outs should ever be placed inside of dust rooms. Switches 
of course must often be placed in such rooms, as in many 
cases the entire building outside of the engine room is dusty. 
In such cases the switches as well as the cut-outs may, how- 
ever, be often placed on the outside walls convenient to some 
window. 

An approved cabinet is shown in Figure 68. If used in 
connection with knife switches it should be large enough to 
admit being closed when the switch is open. In cases where 
cut-outs and switches must be located in dusty rooms, it 
would be well to construct double cabinets^ one part for the 
cut-outs and another for the switches. The fuses, which are 
the most dangerous, can then be tightly enclosed, as it will 
seldom be necessary to get at them. In practice it has been 
found almost impossible to keep the doors of cabinets which 
are much used closed. It seems next to impossible to con- 
struct a cabinet which is dust proof, with a door that can be 
readily opened, and a self-closing door can hardly be made 
to remain dustproof. Doors are made self-closing either 
through gravity or by suitable springs. 

As switch and cut-out boxes are very likely to be used for 
the storage of cotton waste, paper, etc., which would readily 
ignite from a melted fuse, it would be well to construct them 
with a slanting bottom as indicated by the dotted line in Fig- 
ure 69, so tha.t nothing will lie in them. 

c. Must, when exposed to dampness, either be enclosed 
in a waterproof box or mounted on porcelain knobs. 

The cover of the box should be so made that no moisture 
Whicb may collect on the top or sides of the box can enter it. 

Figure 69 is a sectional side view of a cut-out box for use 



CONSTANT CURRENT SYSTEMS. 127 

out of doors. In it the switch is mounted on porcelain knobs. 
In all damp places much trouble is experienced from leakage 
through the moisture on the surface of the slate or marble 
and through the wax used to cover the bare parts on back of 
switch. 

d. Time switches, sign flashers and similiar appliances 
must be of approved design and enclosed in a steel box or 
cabinet lined with fire-resisting material. 

If a steel box is used, the minimum thickness of the steel 
must be 0.128 of an inch (No. 8 B. & S. gage). 

If a cabinet is used, it must be lined with marble or 
slate at least % of an inch thick, or with steel not less than 
0.128 of an inch thick. Box or cabinet must be so constructed 
that when switch operates blade shall clear the door by at 
least one inch. 

Special attention should also be given to the location of 
such switches and flashers. They are often left without care, 
the blades wear down and the arcing continues .through bad 
contacts. Often springs become weak and no longer break the 
circuit properly. 

Time switches are usually operated by clockwork, the clock 
releasing a spring which throws the switch on or off as may 
be required and pre-determined. Complete diagrams of sign 
flashers are given in '^Modern Wiring Diagrams and Descrip- 
tions" and will not be repeated here. 



CONSTANT-CURRENT SYSTEMS. 
18. Principally Series Arc Lighting Wires. 

{See also Nos. 14, 15 and 16.) 

a. Must have an approved rubber insulating covering (see 
No. 41). 

b. Must be arranged to enter and leave the building 



128 



MODERN ELECTRICAL CONSTRUCTION. 



through an approved double-contact service switch (see No. 
51 b), mounted in a non-combustible case, kept free from mois- 
ture, and eas}- of access to police or firemen. 

In order that all of the wiring in the building may be 

entirely disconnected a switch, the principle of which is illus- 




Figure 70. 



trated at d, Figure 70, is provided where wires enter and 
leave the building. A modern commercial form of this switch 
is shown in Figure 71. This switch never breaks the circuit. 
As shown in Figure 70, the current passes from the positive 
pole, through the upper blade of the switch to b and thence 
through the arc lamps back to c and to the negative pole. 
When it is desired to extinguish the lamps the two blades of 
the switch are moved downward, as indicated by the dotted 
lines. The contacts d are arranged so .that both switch blades 
connect with them before disconnecting entirely from the 
points b and c. As soon as both blades are in contact with d 
all current flows through it because the resis.tance of it is so 
very much less than that of the lamps. With the switch in 
the position indicated by dotted lines, the current still flows 
in the outside wires, but all wires within the building are 
"dead." At e, Figure 70, is shown a single-pole switch which 



CONSTANT CURRENT SYSTEMS. 



129 




Figure 71. 



Operates on the same principle as the other. If this switch is 

closed all current will pass through it ; if open the current will 

pass through the last 

lamp. A switch of this 

kind is always arranged 

within the lamp itself. 

This latter way of 

switching lamps should 

never be used, as a lamp 

switched in this way is 

never safe to handle. 

There is just as much 

danger from shocks 

when the lamp is 

switched off as when on. 

With switches as de- 
scribed above there is no 

spark whatever when lamps are switched off, but there is usu- 
ally quite an arc when the lamps are switched in. Should 
there be a broken wire or a lamp out of order in the circuit 
to be switched in, there will be quite an arc maintained for 
some time. In such a case the switch should be quickly closed 
and the trouble located. 

In handling live wires of this system great care is neces- 
sary. The wireman should insulate himself from the ground 
by a dry board, or, if all about him is damp, by a board resting 
on insulators. Rubber gloves and rubber boots, if kept dry, 
are useful. 

Death or bad burns may result if the wireman, standing on 
wet ground or any conductor in connection with it, touches 
part of a circuit which is also partly in connection with the 
ground. If, in Figure 70, the wire at / is grounded, a man in 
connection with the ground and touching a bare wire at h will 



130 MODERN ELECTRICAL CONSTRUCTION. 

receive a shock due to about 50 volts, but if he touches the 
wire at g he will receive a shock of about 150 volts. The 
shock received from a line containing 100 lamps may be any- 
thing from 50 to 5,000 volts, and may result in only a slight 
hurn or in instant death. 

Another danger in connection with live circuits is the lia- 
bility of cutting oneself into circuit. If one is perfectly 
insulated from the ground there is no harm whatever in touch- 
ing one live wire (with very high voltages such insulation is, 
however, hard to obtain) with either one or both hands while 
the wires are in order. Should, however, the wire between 
the two hands break, the current would immediately pass 
through the body, very likely causing ins.tant death. Even if 
the circuit is not entirely broken, if only a resistance is cut in, 
the shock will be very severe. As, for instance, if one should 
touch the terminal of an arc lamp, not burning, with each hand 
nothing whatever would be felt, but, if the lamp were now 
suddenly switched on, .there would be a very severe shock at 
first, which would become less so when the lamps were fairly 
started. To avoid the possibility of such occurrences when 
working on live lamps or circuits a short wire known as a 
"jumper" is often connected, as at k, Figure 70. This will 
carry all current, and there is now no danger except from a 
connection to ground. 

c. Must always be in plain sight, and never encased, ex- 
cept when required by the Inspection Department having 
jurisdiction. 

What is known as concealed knob and tube work is not 
allowed in wiring for H. T. arcs ; neither can the wires be 
run in moulding or conduit. 

It has been customary to use no smaller than No. 6 wire 
for these high tension series circuits. The current required 
is seldom more than 10 amperes, and No. 14 wire has sufficient 



CONSTANT CURRENT SYSTEMS. 131 

carrying capacity, but its mechanical strength is not very 
great. The danger from a broken wire in high tension sys- 
tems is much greater than in low tension systems, because of 
the long arc which occurs at the break. The loss in volts per 
100 feet with No. 6 will be about .4, while with No. 14 it will 
be 2.6. While this will not affect the lights, the pressure at 
the generator being correspondingly increased, the question 
of drop is of importance. On a circuit 10 miles long a No. 
14 wire would have a drop of 1372 volts and a No. 6 wire 
a drop of 211 volts. 

d. Must be supported on glass or porcelain insulators, 
which separate the wire at least one inch from the surface 
wired over, and must be kept rigidly at least eight inches from 
each other, except within the structure of lamps, on hanger- 
boards or in cut-out boxes, or like places, where a less distance 
is necessary. 

An extra precaution often taken in this kind of work on 
plastered walls is to place a wooden block or rosette about 
three inches in diameter and one-half inch thick under each 
insulator; this secures greater separation from ceilings and 
side walls and adds greatly to the stability of the insulators. 
On plastered walls a small insulator, if subjected to side 
strain, will cut into the plaster on one side and allow the 
wires to sag; the wooden block will prevent this. 

e. Must, on side wall, be protected from mechanical injury 
by a substantial boxing, retaining an air space of one inch 
around the conductors, closed at the top (the wires passing 
through bushed holes), and extending not less than seven 
feet from the floor. When crossing floor timbers in cellars, 
or in rooms where they might be exposed to injury, wires 
must be attached by their insulating supports to the under 
side of a wooden strip not less than one-half an inch in thick- 
ness. Tns.tead of the running-boards, guard strips on each 
side of and close to the wires will be accepted. These strips 



132 



MODERN ELECTRICAL CONSTRUCTION. 



K 



!,>• 


T 1 ' 


' P" 1 







. ' JL 




f ' 




"■ 1 








r ^' 1 


.f\ 


^/zI^ljL 


1 


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B^' 


11'"'^ 


1 r 


1*' .y 


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to be not less than seven-eighths of an inch in thickness and 
at least as high as the insulators. 

Except on joisted ceilincrs. a 
strip one-half of an inch thicl<: is 
not considered sufRciently stilt 
and strong-. For spans of say 
eight or ten feet, where there i.s 
but little vibration, one-inch stock 
is generally sutRciently stiff; but 
where the span is longer than tliis 
or there is considerable vibration, 
still heavier stock should be used. 

Figure 72 is an illustration of 
protection on side walls, giving 
the dimensions required. The 
wooden block shown, which raises 
bushings above floor, is an extra 
protection to prevent water from 
running into them. 



Figure 

19. Series Arc Lamps. 

(For construction rules, see No. 57.) 

a. Must be carefully isolated from inflammable material. 

h. Must be provided at all times with a glass globe sur- 
rounding the arc, and securely fastened upon a closed base. 
Broken or cracked globes must not be used. 

c. Must be provided with a wire netting (having a mesh 
not exceeding one and one-fourth inches) around the globe, 
and an approved spark arrester (see No. 58), when readily 
inflammable material is in the vicinity of the lamps, to prevent 
escape of sparks of caYbon or melted copper. It is recom- 
mended that plain carbons, not copper-plated, be used for 
lamps in such places. 

Outside arc lamps must be suspended at least eight feet 
above sidewalks. Inside arc lamps must be placed out of 
reach or suitably protected. 

Arc lamps, when used in places where they are exposed to 




CONSTANT CURRENT SYSTEMS. 



133 



flyings of easily inflammable material, should have the car- 
bons enclosed completely in a tight globe in such manner as 
to avoid the necessity for spark arresters. 

"Enclosed arc" lamps, having tight inner globes, may be 
used, and the requirements of sections b and c above would, 
of course, not apply to them, except that a v^ire netting 
around the inner globe may in some cases be required if the 
outer globe is omitted. 

d. Where hanger-boards (see No. 56) are not used, lamps 
must be hung from insulating supports other than their con- 
ductors. 

At the left, Figure 73, is shown the usual method of sus- 
pending outdoor arc lamps on buildings. The supporting wire 
may be fastened to brick or stone walls by drilling a hole 
about four inches deep and plugging this securely with wood, 
when an eye or lag bolt or large spike may be driven or 
screwed into it. Expansion bolts, of which -there are many 
kinds to be had, may also be used. Lt is best to arrange the 




Figure 73. 



supporting wires at quite a high angle, otherwise the direct 
outward pull may be too great. Some of the older arc lamps 
are not provided with insulators, and may be suspended, as 
shown in the center of the figure. On very low ceilings, 
lamps are often arranged as shown at the right, the plastering 



134 MODEKN ELECTKICAL CONSTRUCTION. 

being cut away and lamp suspended from floor above joists. 
The space eibove plaster must be enclosed on all sides and all 
woodwork protected with asbestos board at least one-eighth 
inch thick. 

If this method is used with constant potential arc lamps 
carrying resistance in the hood, it would be well to remove 
or short-circuit this resistance and locate another in a more 
suitable place. 

e. Lamps when arranged to be raised and lowered, either 
for carboning or other purposes, shall be connected up with 
stranded conductors from the last point of support to the 
lamp, when such conductor is larger than No. 14 B. & S. 
gage. 

20. Incandescent Lamps in Series Circuits. 

a. Must have the conductors installed as required in No. 
18, and each lamp must be provided with an automatic cut-out. 

h. Must have each lamp suspended from a hanger-board 
by means of rigid tube. 

c. No electro-magnetic device for switches and no mul- 
tiple-series or series-multiple system of lighting will be ap- 
proved. 

d. Must not under any circumstances be attached to gas 
fixtures. 



CONSTANT-POTENTIAL SYSTEMS. 

GENERAL RULES — ALL VOLTAGES. 

21. Automatic Cut-Outs (Fuses and Circuit-Breakers). 

{See No. 17, and for construction, Nos. 52 and 53.) 

Excepting- on main .switchboards, or where otherwise sub- 
ject to expert supervision, circuit-breakers will not be ac- 
cepted unless fuses are also provided. 

The fuse is the principal protective device used in elec- 



CONSTANT POTENTIAL SYSTEMS. 135 

trie light and power work. In its simplest form it consists of 
a piece of wire made of a certain alloy designed to melt at 
a comparatively low temperature. It is so connected in the 
circuit that all the current must pass through it. We 
have already seen that currents of electricity generate heat in 
the conductors .through which they pass, and that this heat 
is proportional to the square of the current flowing; that is, 
if we double the current we shall increase the production of 
heat fourfold. A dangerous rise in current strength may be 
due to a "short circuit" or to an overload, too many lamps 
or motors being connected to a circuit. To prevent damage 
to wires and other apparatus from excessive currents, fuses 
or cut-outs must be installed. When the current rises above 
its allowed strength the fuse melts and opens the circuit; 
that is, stops all current flow. The melting of the fuse is 
accompanied by a flash of fire due to the arc which is set up 
across the break in the fuse wire. On an ordinary overload 
with the smaller size fuses this arc may not be very severe, 
but with the larger size fuses and on short circuits a very 
severe flash and explosion may result and molten metal may 
be thrown for some distance from the fuse. This explosion 
is caused by the outer layers of metal of the fuse remaining 
cool and in a solid state while the metal at the center of the 
fuse is first melted and then vaporized. 

Another device which is used for the same purpose as the 
fuse is known as the circuit-breaker. A circuit-breaker 
in its simplest form comprises a knife switch which when 
closed is forced in against a spring and held in place by 
means of a small catch. A solenoid, inside of which is placed 
a moveable iron core, is connected in series with one side of 
the switch. When the current passing through this solenoid 
exceeds a certain amount, the iron core is drawn up into it, 



136 MODERN ELECTRICAL CONSTRUCTION. 

and, striking against the catch, releases the switch which will 
then fly open, thus cutting off the current. The core of this 
solenoid is so designed that when it starts to move its speed 
is greatly accelerated so that it strikes the catch a sharp 
blow. By means of a small adjusting screw the circuit-break- 
er can be set to operate at various current strengths within 
its limits. For this reason and for the further reason that 
it is so easily made inoperative by tying or blocking its sol- 
enoid it is not approved for general use unless fuses are also 
installed. It may be used under the care of a competent elec- 
trician who understands the dangers of its abuse. 

Under these conditions its use is to be strongly recom- 
mended. Where not so used fuses must also be provided in the 
same circuit with the circuit breaker. For further information 
in reference to the use of circuit breakers see section on Genera- 
tors, Page 58. 

a. Must be placed on all service wires, either overhead 
or underground, as near as possible to the point where they 
enter the building and inside the walls, and arranged to cut 
off the entire current from the building. 

Where the switch required by No. 22 a is inside the build- 
ing, the cut-out required by this section must be placed so as 
to protect it. 

For three-wire (not three-phase) systems the fuse in the 
neutral wire may be omitted, provided the neutral wire is of equal 
carrying capacity to the larger of the outside wires, and is 
grounded as provided for in No. 13 A. 

In risks having private plants, the yard wires running 
from building to building are not generally considered as 
service wires, so that cut-outs would not be required where 
the wires enter buildings, provided that the noxt fuse back 
is small enough to properly protect the wires inside the build- 
ing in question. 

The fuse block here required serves a double purpose ; it 
affords protection to the whole installation while in use, and 




CONSTANT POTENTIAL SYSTEMS. 137 

is an effective means of disconnecting a building when cur- 
rent is no longer used. This can also be accomplished by 
means of the service switch, bat a switch 
is so easily closed by any one that it must 
never be relied upon entirely for this 
purpose. 

Figure 74 shows arrangement of fuses 
and switch as commonly installed where 
wires enter buildings. The wires enter at 
the top, connect to the fuse terminals, cur- 
rent passing through the fuses to the 

switch. 

Figure 74. 
This rule allows the neutral fuse to be 

omitted on three-wire systems where the neutral is grounded 
and where the neutral wire is of as great carrying capacity 
as the larger of the outside wires. On three-wire systems 
where the neutral wire is not grounded, as in the case of some 
isolated plants, fuses must be placed in all three wires, includ- 
ing the neutral wire. The reason for this is obvious. A 
ground coming on any part of the neutral wire of a three- 
wire grounded system cannot cause a short circuit. Referring 
to Figure 75, g shows the permanent ground and b a ground 
on any other point on the neutral wire. It is plain that the 
ground b cannot cause a short circuit, and the fuse in this 
wire may, therefore, be omitted. A ground coming on 
either of the outside wires, at A for instance, would be cleared 
by the fuse protecting that wire. In a system with an un- 
grounded neu.tral a single ground coming on one of the out- 
side wires, as at g' for instance, would not cause a short cir- 
cuit, but if the outside wire was grounded at g' and a ground 
should come on the neutral wire, at b for instance, a short 
circuit would immediately result and the neutral wire would 



138 



MODERN ELECTRICAL CONSTRUCTION. 



probably be destroyed owing to the fact that there is no fuse 
to protect it. 

If the fuse is omitted in the neutral wire and a fuse on 
one of the outside mains should blow, the neutral wire would 
then be called upon to carry the same amount of current as 
was being carried in the remaining outside wire. For this 
reason the neutral wire must be of as great carrying capacity 
as the larger of the outside wires. 



G'i 



'^-<\> 



-^ 



+ ± - 

Figure 75 

The danger arising from the blowing of the neutral fuse 
(which this rule is designed to prevent) is described under 
the next rule, 21 b. 

b. Must be placed at every point where a change is made 
in the size of wire [unless the cut-out in the larger wire will 
protect the smaller (see Table of Carrying Capacity)]. 

For three-wire (not three-phase) systems. the fuse in the 
neutral wire, except that* called for under No. 21 rf, may be 
omitted, provided the neutral wire is of equal carrying capacity 
to the larger of the outside wires, and is grounded as provided for 
in No. ISA. 

Figure 76, A to D, shows systems of distribution and ar- 
rangement of mains in general use. Figure A shows the 



CONSTANT POTENTIAL SYSTEMS. 139 

simplest and cheapest method of running mains, and is known 
as the "tree system." Beginning at the service the wires 
must be large enough to carry the whole amount of current 
used to the first floor or wherever the first cut-out center is 
located. At this point the size of wire may be reduced be- 
cause it will be required to carry only the current used further 
on. Main cut-outs should be arranged as shown in the figure 
at 1 and 2. That is, the cut-outs protecting the mains must 
be installed in the mains at each floor after the current for 
that floor has been taken off. Cases are often found where 
the cut-out is placed in the main line, ahead of the hranch 
blocks. This is obviously wrong, as the fuse will have to be 
too heavy to protect the smaller mains. 

Figure B shows a somewhat different arrangement which 
requires more wire and is more expensive in the beginning, 
but far more satisfactory and economical in operation. With 
the wires arranged as shown in the diagram the pressure at 
all the lamps will be nearly uniform. Even if the mains are 
designed for a considerable loss to the center of distribution 
the dynamo may be made to compensate for this loss and 
keep the lamps burning properly. With the tree system, A, 
this is impossible; the lamps at the first cut-out center will 
either be too bright or those at the last center too dim. 

Figure C shows a convertible three-wire system. 

In order to convert a three-wire system into a two-wire 
system the two outside wires are joined together. The mid- 
dle wire then forms one side of the system and the outside 
wires the other. The middle wire must carry as much cur- 
rent as both outside wires combined and should have a carry- 
ing capacity equal to them. It should be remembered that a 



140 



MODERN ELECTRICAL CONSTRUCTION. 



zgiii^ 




Figure 76. 



CONSTA.NT POTENTIAL SYSTEMS. 141 

wire containing simply twice as many circular mils does not 
fulfill this requirement, as is shown in Table No. I on page 312, 
which must be consulted in selecting wires. 

In three-wire systems the middle or neutral wire is merely 
a balancing wire and normally carries very little or no cur- 
rent, but it is very important that it remain intact. If for in- 
stance in Figure D the branch circuit a has twelve lights 
burning w^hile there are also twelve lights burning on b, the 
current will pass from the positive wire through the lower 
fuse to c7. through the twelve lights in a back to the middle 
fuse, thence through the twelve lights in b to the upper fuse 
and negative wire, the two sets of lamps burning in series. 
If now the lamps in b are switched off the current from a can 
no longer pass through them and instead returns through the 
middle fuse to the neutral wire. If only six lights in b are 
burning, while twelve are burning in a, the current of six 
lights will return over the negative wire and the other six 
in a will return over the neutral wire. Should the neutral 
wire be broken or its fuse blown there would be no return 
path on it for the extra current, and consequently the cur- 
rent passing through the twelve lights in a would be forced 
to pass through the six lights in b, causing them to burn 
with excessive brilliancy and to break in a very short time. 
Should a short circuit occur, say on circuit b, wath the neu- 
tral wire intact, it would merely blow out a fuse, but if the 
main neutral fuse were out it w^ould bring 220 volts on cir- 
cuit a and speedily cause damage to the lamps. Thus it 
will be seen that it is of great importance to fuse the neutral 
w^ire so that it will not easily blow^ out. 

Figure C shows a system of wiring quite often used. A 
set of heavy mains are run from the service or dynamo to 
the top floor and taps taken off at each floor. These mains 
do not change size at each floor, but are continuous for their 



142 



MODERN ELECTRICAL CONSTRUCTION. 



entire length. While this method has some of the objections 
of the tree system in regard to voltage, still the faults of the 
tree system are greatly reduced owing to the much smaller 
losses in the mains between the upper floors, or those farthest 
from the dynamo. 

Figure 11 shows .the method of fusing main switch and 
branch circuits. The switch itself wall require a fuse to pro- 
tect it, although it need not be right at the switch. 

It often becomes necessary to reinforce a set of mains, 
especially for motors, w^hich have become overloaded, by run- 
ning another wire in parallel with the old, as indicated in 
Figures 78 and 79. Two separate and distinct ways of ar- 









Fig. 77. 



Fig. 78. Fig. 79. 



Fig. 80. 



ranging them are shown and it depends upon the conditions 
as to w^hich is preferable. If the wares are small or run in 
places where they are liable to be broken, the plan shown in 
Figure 78 is the better. Here each wire is properly fused and 
if one breaks the other carries the whole load until its fuse 
melts. If the wires, as often happens, are much overfused, 
the breaking of one wire would force the other to carry 



CONSTANT POTENTIAL SYSTEMS. 143 

the whole current and become overheated. If the arrange- 
ment were as in Figure 79 the unbroken wire would carry the 
current indefinitely and soon become overheated. On .the 
other hand, if both wires are large and the run is short the 
fuses arranged as in Figure 78 may, through poor contacts, 
prevent one or the other of the wires from obtaining its 
full share of the current. The fuse making poor contact 
would force a much greater share of current through the 
other wire. In most cases the better plan would be to ar- 
range the wires as in Figure 79. If the current supplied is 
for lights the branch cut-outs can be separated and each set 
of mains allowed to supply a certain part of them, when 
each set should be made independent. For sizes of wires .to 
be used for reinforcing, see Tables. 

With the three-wire system where"^ a larger motor load 
and a few lights are run the lights are often fused as shown 
in Figure 80, a small wire being run for the neutral, this 
smaller wire, of course, being properly fused at the main cut- 
out. Plug cut-outs of the .type shown in this figure often 
have the metal parts projecting above the porcelain; they 
should be connected so that the metal parts which project are 
dead when the plugs are removed. This will prevent many 
short circuits on disconnected cut-outs. 

Figure 81 shows the method of converting a two-wire 
system into a three-wire system with one extra wire to run. 
This extra wire will very likely not need to be as large as the 
other wires are, because the three-wire system requires only 
one-half as much current and it should, therefore, be used as 
the neutral. This arrangement will secure the full benefit of 
all the copper in the old wires (which are probably much 
larger than necessary) and will operate at a very small loss. 

Figure 82 shows a straight three-wire system changed to 
a two-wire system, one extra wire run for it. If the three 



144 



MODERN ELECTRICAL CONSTRCCTION. 



wires are of the proper capacity the addition of the fourth 
wire as in the figure will make it correct for two-wire sys- 




Figure 81. 



Figure 82. 



Fig-ure 83. 



terns, the mains feeding the upper and lower groups being, of 
course, properly fused where they start. 

In Figure 83 the cut-outs are so connected that all branch 
wires leaving the cut-out box at either side are of the same 
polarity. This is often useful where many wires are to be 
run close together. 

c. Must be in plain sight, or enclosed in an approved 
cabinet (see No. 54), and readily accessible. They must not 
be placed in the cano^Jies or shells of fixtures. 

The ordinary porcelain link fuse cut-out will not be ap- 
proved. Link fuses may be used only when mounted on slate 
or marble bases conforming- to No. 52, and must be enclosed 
in dust-tight, fireproofed cabinets, except on switchboards 
located well away from combustible material, as in the ordi- 



CONSTANT POTENTIAL SYSTEMS. 1^ 

nary engine and dynamo room and where these conditions will 
be maintained. 

While it is required that cut-out cabinets be accessible 
there is also danger in making them too accessible, for such 
cabinets are very often used for storage of paper or cotton 
waste. It would seem that about seven feet above the floor 
is the most desirable height to place them or the cabinet 
may be arranged with a slanting bottom which will make it 
impossible to store anything in it. It is also well to locate 
the cut-out cabinet away from inflammable material, for long 
experience has shown that doors are nearly always left open. 
Especially is this the case when switches are in the same 
cabinets with the cut-outs. 

d. Must be so placed that no set of incandescent lamps 
requiring more than 660 watts, whether grouped on one fix- 
ture or on several fixtures or pendants, will be dependent 
upon one cut-out. Special permission may be given in writ- 
ing by the Inspection Department having jurisdiction for 
departure from this rule, in the case of large chandeliers. 
(For exceptions, see No. 31 A, b, 3 [h] and 4 [h] for bor- 
der lights, see List of Fittings for rules for electric signs.) 
All branches or taps from any three-wire system which are 
directly connected to lamp sockets or other translating de- 
vices must be run as two-wire circuits if the fuses are omitted 
in the neutral, or if the difference of potential between the 
two outside wires is over 250 volts, and both wires of such 
branch or tap circuits must be protected by proper fuses. 

The above rule shall also apply to motors when more than 
one is dependent on a single cut-out. 

The fuses in the branch cut-outs should not have a rated 
capacity greater than 6 amperes on 110 volt systems and 3 
amperes on 220 volt systems. 

The idea is to have a small fuse to protect the lamp socket 
and the small wire used for fixtures, pendants, etc. It also 
lessens the chances of extinguishing a large number of lights 
if a short circuit occurs. 

*'On open work in large mills approved link fused rosettes 
may be used at a voltage of not over 125 and approved enclosed 
fused rosettes at a voltage of not over 250, the fuse in the 



146 MODERN ELECTRICAL CONSTRUCTION. 

rosettes not to exceed 3 amperes, and a fuse of over 25 amperes 
must not be used in the branch circuit." 

e. The rated capacity of fuses must not exceed the allow- 
able carrying capacity of the wire as given in No. 16. Cir- 
cuit-breakers must not be set more than 30 per cent above 
the allowable carrying capacity of the wire, unless a fusible 
cut-out is also ins.talled in the circuit. 

In the^ arms of fixtures carrying a single socket a No. 18 
B. & S. gage wire supplying only one socket will be considered 
as properly protected by a six ampere fuse. 

A 16 c. p. incandescent lamp is usually estimated at 55 
watts and consequently the number of lamps allowed on one 
circuit is usually twelve, whether 110 or 220 volts are used. 
If voltages lower than 110 are used the current required by 
twelve 55 watts lamps will be too great, and fewer lamps 
should be used per circuit. Although a number of small fan 
motors may be run on one circuit each motor should be pro- 
vided with a switch ; as a rule such a switch is on the motor. 

22. Switches. 

(See No. 17, and for construction, No. 57.) 

a. Must be placed on all service wires, either overhead 
or underground, in a readily accessible place, as near as 
possible to the point where the wires enter the building and 
arranged to cut off the entire current. 

Service cut-out and switch must be arranged to cut off 
current from all devices including meters. 

In risks having private plants the yard wires running 
from building to building- are not generally considered as 
service wires, so that switches would not be required in 
each building if there are other switches conveniently located 
on the mains or if the generators are near at hand. 

In overhead construction the best plan is to locate the 
switch at either front or rear of building so that wires may 
lead to it direct from pole. Avoid rnnning wires on sides 
of building where it is likely that other bmldings may be 
erected. In underground construction, where the space under 



CONSTANT POTENTIAL SYSTEMS. 147 

sidewalk and basement is not occupied, it is advisable to place 
a cut-out where wires enter the building from street and 
to locate the service switch in a more accessible place. 

Although the rules do not call for switch to be installed 
in each separate building in the case of large plants, still 
it is o£ten advisable to install them, for in case of trouble 
it is necessary that the current can be immediately shut off. 
A switch is also useful in cases of trouble on the wiring, to 
allow of repairing. 

b. Must always be placed in dry, accessible places, and 
be grouped as far as possible. (See No. 17 c.) Single- 
throw knife switches must be so placed that gravity will tend 
to open rather than close them. Double-throw knife switches 
may be mounted so that the throw will be either vertical or 
horizontal as preferred. 

When possible, switches should be so wired that blades 
will be "dead" when switch is open. 

If switches are used in rooms where combustible flyings 
would be likely to accumulate around them, they should be 
enclosed in dust-tight cabinets. (See note under No. 17 b.) 
Even in rooms where there are no combustible materials it is 
better to put all knife switches in cabinets, in order to lessen 
the danger of accidental short circuits being made across their 
exposed metal parts by careless workmen. 

Up to 250 volts and thirty amperes, approved indicating 
snap switches are advised in preference to knife switches 
on lighting circuits about the workrooms. 

To comply with this rule will ordinarily bring the fuses 
of knife switches directly under the handle of switch. If 
there happens to be a 'short circuit on the wires when switch 
is closed the fuses will blow instantly and very likely burn 
the operator's hand. In connection with such switches car- 
tridge fuses should be used or the switches, especially the 
larger ones, closed by pushing them in with a stick. The 
danger from opening a switch is much less. 

Figure 84 shows a switch arranged to comply with all 
three points of this rule, the feed wires coming from below. 



148 



MODERN ELECTRICAL CONSTRUCTION. 



This requires that incoming and outgoing wires pass each 
other. In this case, the wires pass each other behind the 




Figure 84. 



Figure 85. 



switch base, they being encased in flexible tubing. A side 
view is also given in Figure 85. Instead of passing behind 
the switch the wires may, of course, run around one side to 
the .top, the other wires around the other side to the bot- 
tom. 

Figure 85 illus.trates a cabinet so arranged that the switch 
within can be opened or closed without opening the cabinet. 
The cover is hinged at the top, and slotted in the center, 
which leaves room for .the lever by which the switch is 
worked to adjust itself so it will always be out of the way. 
A switch which is often used may as well be left without 
a cover as with one, fgr the door must be opened or closed 
every time the switch is used, and the cabinet will always 
be found open. Figure 85 will answer where only protection 
agains.t accidental contacts is required. 

c. Single pole switches must never, be used as service 



CONSTANT POTENTIAL SYSTEMS. 



149 



switches nor placed in the neutral wire of a three-wire sys- 
tem, except in the two-wire branch or tap circuit described 
in 21, d. 

This, of course, does not apply to the grounded circuits 
of street railway systems. 

Three-way switches are considered as single pole switches 
and must be wired so that only one pole of the circuit is 
carried to either switch. 

This rule allows the use of single pole switches on circuits 
of 660 watts, 6 amperes at 110 volts, or 3 amperes at 220 
volts, which corresponds roughly to twelve 16 c. p. lamps. 
In systems that are not grounded a single pole switch will 




Figure 86. 

answer fairly well if large enough. It will readily open the 
circuit and it offers no opportunities for short circuits, as do 
double pole switches. Where, however, three-wire systems 
with grounded neutrals are used double-pole switches are 
preferable, for by reference to Figure 86 one can readily see 
that if the neutral or middle wire is grounded (which is 
equivalent to being in connection with gas piping) and an- 
other ground should come onto the wiring say at a, the single- 
switch, S, would not control the lights at all. The current 
would flow from the positive wire to the top fuse, through the 
twelve lights to ground a, through the ground to the neu- 
tral or middle wire and back to the dynamo, regardless of 
whether the switch is on or off. Also, a man working at the 
lights could easily make a short circuit by bringing the wires 



150 MODEKN ELECTKICAL CONSTKUCTION. 

into contact with the gas piping even if the switch were turned 
off. When single-pole switches are used in connection with 
such circuits they should never be placed in the neutral wire 
as in the diagram. If the switch S were placed in the top 
wire .these troubles would be avoided. Often times, how- 
ever, switches are connected before the circuits are run into 
cut-outs and an attempt to place single-pole switches on a 
certain wire requires considerable care, which many wire- 
men will not take. In the case of only two wires from a 
central, three-wire, station being run iato a building, the 
neutral wire is not known until meters are set and instruc- 
tions would, therefore, have to be left for meter men which 
would often be disregarded, so that in all cases on three- 
wire grounded systems double-pole switches are preferable. 

Three-way switches must not be used on circuits of over 
660 watts. In wiring up three-way switches if both poles 
of the circuit are brought to the switch only one wire need 
be run between the switches, but where bath poles of the 
circuit are connected into the switch the arc produced on 
operating the switch may carry from one pole to the other 
and cause a short circuit so that this method of wiring should 
never be used. 

For full and comprehensive description of ''three-way" 
switches the reader is referred to ''Modern Wiring Diagrams 
and Descriptions" by the authors of this work. 

d. Where flush switches or receptacles are used, whether 
with conduit systems or not, the switches must be enclosed in 
boxes constructed of iron or steel. No push buttons for bells, 
gas-lighting circuits, or ^the like shall be placed in the same 
wall plate with switches controlling electric light or power 
wiring. 

This requires an approi'ed box in addition to the porcelain 
enclosure of the switch or receptacle. 

e. Where possible, at all switch or fixture outlets, a 



CONSTANT POTENTIAL SYSTEMS. 



151 



%-inch block must be fastened between studs or floor tim- 
bers flush with the back of lathing to hold tubes and to 
support switches or fixtures. When this cannot be done, 
wooden base blocks, not less than ^-inch in thickness, se- 
curely screwed to lathing must be provided for switches, and 
also for fixtures which are not attached to gas pipes or con- 
duit tubing. 

The above will not be necessary where outlet boxes are 
used which will give proper support for fixtures, etc. 

Figure 87 shows concealed wiring back of lathing leading 
to a double-pole flush switch. The board fastened between 
studdings must be cut out to admit the box of switch and 



j_j_ 



li. 




TT 





Figure 87. 



Figure 88. 



the size of this box should be known when wires are put in. 
The board should not rest hard against the lathing, but 
leave a little space for plaster to work in behind the lath. 
Loom is put on all wires at outlets and must extend back 
to the nearest knob. 

Figure 88 shows two methods of fastening snap switches 
by means of wooden blocks first fastened to the plaster. One 
block is cut out so as to bring all wires under the switch 
and entirely conceal them. The opening in block to admit 



152 MODERN ELECTRICAL CONSTRUCTION. 

wires and bushings should be oblong, so as to leave room 
on two sides for the screw^s wath which the switch is to be 
fastened. On the other block the wires and bushing are 
brought through close to the outer edge of switch base. 
By careful workmanship a neat job can be done in this w^ay. 
As most snap switches cross conductors, that is, connect 
points a and h, if from the nature of the case it becomes 
necessary to run any of the wires close together these two 
wares may be run that way, for they can never be of oppo- 
site polarity. 

f. Sub-bases of non-combustible, non-absorptive insulat- 
ing material, which will separate the wires at least Yz inch 
from the surface wired over, must be installed under all snap 
switches used in exposed knob and cleat work. Sub-bases 
must also be used in moulding work, but they may be made of 
hardwood. 

23. Electric Heaters. 

It is often desirable to connect in multiple with the heaters 
and between the heater and the switch controlling same an 
incandescent lamp of low candle power, as it shows at a 
glance whether or not the switch is open and tends to pre- 
vent its being left closed through oversight. Inspection De- 
partments having jurisdiction may require this provision to 
be carried out if they deem it necessary. 

a. Must be protected by a cut-out and controlled by in- 
dicating switches. Switches must be double pole except when 
the device controlled does not require more .than 660 watts 
of energy. 

h. Must never be concealed, but must at all times be in 
plain sight. 

Special permission may be given in writing by the In- 
spection Department having jurisdiction for departure from 
this rule in certain cases. 

c. Flexible conductors for smoothing irons and sad irons 
and for all devices requiring over 250 w^atts must complv with 
No. 45, g, ^ ^ 

d. For portable heating devices the flexible conductors 
must be connected .to an approred plug device, so arranged 



CONSTANT POTENTIAL SYSTEMS. 



153 



that the plug will pull out and open the circuit in case any 
abnormal strain is put on the flexible conductor. This device 
may be sationary or it may be placed in the cord itself. The 
cable or cord must be attached to the heating apparatus in 
such manner that it will be protected from "kinking, chafing 
or like injury at or near the point of connection. 

e. Smoothing irons, sad irons, and other heating appliances 
that are intended to be applied to inflammable articles, such 
as clothing, must conform to the above rules so far as they 




Figure 89. 



apply. They nuist also be provided with an approved stand, 
on which they should be placed when not in use. 

An approved automatic attachment which will cut off the 
current when the iron is not on the stand or in actual use is 
desirable. Inspection Departments having jurisdiction may re- 
quire this provision to be carried out if they deem it ad- 
visable. 

/. Stationary electric heating apparatus, such as radia- 
tors, ranges, plate warmers, etc., must be placed in a safe 
location, isolated from inflammable materials, and be treated 
as sources of heat. 

Devices of this description will often require a suitable 
heat-resisting- material placed between the device and its sur- 



154 MODEKN ELKCTEICAL CONSTRUCTION. 

Foundings. Such protection may best be secured by installing 
two or more plates of tin or sheet steel with a one-inch air 
space between or by alternate layers of sheet steel and 
asbestos with a similar air space. 

g. Must each be provided with name-plate, giving the 
maker's name and the normal capacity in volts and amperes. 

In Figure 89 is given a diagram of a heater circuit with 
a 4 c. p. lamp in circuit. Where there are many irons in use, 
as in some tailoring establishments, it is advisable to run 
them all from one set of mains with a main switch conveni- 
ent to exit door and have this switch opened whenever the 
irons are not in use. The individual switch at each iron 
should be located as near as possible to each iron. Cords 
feeding irons or cloth cutting machines are often installed 
as shown, insulators are strung on a tight wire and the cord 
tied to them. This allows considerable latitude in moving 
the iron. 



LOW rOTENTIAL SYSTEMS. 155 

LOW-POTENTIAL SYSTEMS. 

550 Volts or Less. 

Any circuit attached to any machine, or combination of ma- 
chines, which develops a difference of potential between 
any two wires, of over ten volts and less than 550 volts, 
shall be considered as a low-potential circuit, and as dom- 
ing un'der this class, unless an approved transforming de- 
vice is used, which cuts the difference of potential down 
to ten volts or less. The primary circuit not to exceed a 
potential of 3,500 volts unless the primary wires are in- 
stalled in accordance with the requirements as given in 
No. 12 A, or are underground. 

For 550 volt motor equipments a margin of ten per cent above 
the 550 volt limit will be allowed at the generator or 
transformer. 

Before pressure is raised above 300 volts on any previous- 
ly existing system of wiring the whole must be strictly 
brought up to all of the requirements of the rules at date. 

24. Wires. 

GENERAL RULES. 

(See also Nos. 14, 15 and 16.) 

a. Must be so arranged that under no circumstances will 
there be a difference of potential of over 300 volts between 
any bare metal parts in any distributing switch or cut-off 
cabinet, or equivalent center of distribution. 

This rule is not intended to prohibit the placing of 
switches or single pole cut-outs for motor systems of voltage 
above 300 in cabinets, but would require that the cabinets be 
divided by approved barriers so arranged that no one section 
shall contain more than one switch nor more than one single 
pole cut-out. 

This rule, as far as it applies to lighting systems or pres- 
sures higher than 300 volts, contemplates a three-wire system 
on which, instead of the customary 110 volts on each side 



156 



MODERN ELECTRICAL CONSTRUCTION. 



of the neutral, 220 volts are used, making a pressure of 440 
volts between the two outside wires. 

The ordinary 110-220 volt, three-wire system will require 
to be changed at cut-out centers as shown in Figure 90, where 



^■4n — g 



2»0 -, 



—440^ 



■2ao— 1 



Figure 90. 



£ 



p=i=at> -- 



ypniQpj ^ 



X3 



2210 



it will be seen a difference of potential greater than 220 volts 
cannot be found within any cut-out box, or at any switch or 
cut-out. 

Special attention should be given to the balancing of the 
load with this arrangement of wiring and both sides of the 
system should be brought into every room or hall requiring 
more than one circuit. False ideas of economy should not 
induce one to arrange large groups of lamps on one side of 
the system in order to save a few cut-out boxes. 

b. Must not be laid in plaster, cement, or similar finish, 
and must never be fastened with staples. 

c. Must not be fished for any great distance, and only in 
places where the inspector can satisfy himself that the rules 
have been complied with. 

Figure 91 illustrates a very common combination of "fish" 
and "moulding" work. Moulding is used to bring the wires 
from the floor to the ceiling and along the ceiling to a point 
Opposite the outlet and parallel with the joists. From this 



LOW POTENTIAL SYSTEMS. 



157 



point to the fixture the wires can then be readils' fished. 

The connection between the fish and moulding work should 
be made as shown at the right, where the moulding is cut 
out so as to admit the loom. It is better, even, to have the 



s \ \ \ \ \ \ \ \ I f 




Figure 91. 

loom show to some extent than to have the wire come in 
contact with the plaster, as will very likely be the case if the 
loom is not fully brought through. 

d. Twin wires must never be used, except in conduits, or 
where flexible conductors are necessary. 

Flexible conductors are in general considered necessary 
only with pendant sockets, certain styles of adjustable brack 



158 



MODERN ELECTRICAL CONSTRUCTION. 



ets, portable lamps, motors and stage plugs, or heating ap- 
paratus. 

e. Must be protected on side walls from mechanical in- 
jury. When crossing floor timbers in cellars, or in rooms 
where they might be exposed to injury, wires must be at- 
tached by their insulating supports to the under side of a 
w^ooden strip, not less than ^ inch in thickness and 
not less than three inches in width. Instead of the running 
boards, guard strips on each side of and close to the wires 
will be accepted. These strips to be not less than seven-eighths 
of an inch in thickness and at least as high as the insulators.- 

Suitable protection on side walls should extend not less 
than five feet from the floor. This may be secured by sub- 
stantial boxing, retaining an air space of one inch around 
the conductors, closed at the top (the wires passing through 
bushed holes) or by approved metal conduit, or pipe of 
equivalent strength. 

When metal conduit or pipe is used, the insulation of each 
wire must be reinforced by approved flexible tubing extending 
from the insulator next below the pipe to the one above it, 
unless the conduit is installed according to No. 25 (sections 
c and f excepted), and the wire used complies with No. 47. 
The two or more wirea of a circuit, each with its flexible tubing 



^V^'^^\\\\\v\\\\\v\\\n\\n\\\\M \ . 1 I . I .ffM/ ' / a// / / ////•///.//////// 




/l^L. 






Figure 92. 

(when required), if carrying alternating current must, or if direct 
current, may be placed within the same pipe. 

In damp places! the wooden boxing may be preferable be- 
cause of the precautions which would be necessary to secure 
proper insulation if the pipe were used. With this exception, 
however, iron piping is considered preferable to the wooden 



LOW POTENTIAL SYSTEMS. 159 

boxing, and its use Is strongly urged. It is especially suit- 
able for the protection of wires near belts, pulleys, etc. 

f. When run in unfinished attics, will be considered as 
concealed, and when run in close proximity to water tanks 
or pipes will )3e considered as exposed to moisture. ' 

In unfinished attics wires are considered as exposed to 
mechanical injury, and must not be run on knobs on upper 
edge of joists. 

Figure 92 illustrates the meaning of the rule in regard 
to wires run along low ceilings. 

Figure 93 gives the dimensions necessary for boxing wires 
on side walls. At the right, the side wall protection consists 
of conduit; a junction box with the lower side knocked out 
is used to enclose bushings. When the cover is screwed on 
the wires are completely enclosed. 

SPECIAL RULES. 

For Open Work. 

In dry places. 

g. Must have an approved rubber, slow-burning weather- 
proof, or slow-burning insulation (see Nos. 41, 42 and 43). 

A slow-burning covering, that is, one that will not carry 
Are, is considered good enough where the wires are entirely 
on insulating supports. Its main object is to prevent the 
copper conductors from coming accidentally into contact with 
each other or anything else. 

h. Must be rigidly supported on non-combustible, non- 
absorptive insulators, which will separate the wires from each 
other and from the surface wired over in accordance with the 
following table : 

Voltage. Distance from Distance between 

Surface. Wires. 

to 300 Va inch 2^ inch 

300 to 550 1 inch 4 inch 

Rigid supporting requires, under ordinary conditions, where 
\\'iring along* flat surfaces, supports at least every four and 
one-half feet. If the wires are liable to be disturbed, the dis- 
tance between supports should be shortened. In buildings or 



160 



MODERN ELECTRICAL CONSTRUCTION. 



mill constrnction, mains of No. 8 B. &: S. gag'e wire or over, 
where not liable to be disturbed, may be separated about six 
inches, and run from timber to timber, not breaking- around, 
and may be supported at each timber only. 

This rule will not be interpreted to forbid the placing: of 
the neutral of an Edison three-wire system in the center of a 




Figure 93. 

three-wire cleat where the difference of potential between the 
outside wires is not over 300 volts, provided the outside wires 
are separated two and one-half inches. 

Figure 94 shows different methods of running wires in 
buildings of mill construction. If the method shown at a is 
used, a few insulators should be placed here and there and the 
wires tied to them to prevent sagging. The arrangements 
shown at b and c are suitable for small wires on high ceil- 
ings. 

The methods shown at d and e are sometimes used where 



LOW POTENTIAL SYSTEMS. 



161 



there is no danger of interference. With long spans, supports 
as shown at / may be used. 




a 



* 



Figure 94. 

Ill damp places, or buiMings specially subject to moisture or 
to acid or other fumes liable to injure the wires or their 
insulation, 

i. Must have an approved insulating covering. 

For protection against water, rubber insulation must be 
used. For protection against corrosive vapors, either weather- 
proof or rubber insulation must be used. (See Nos. 41 and 44.) 

/. Must be rigidly supported on non-combustible, non-ab- 
sorptive insulators, which separate the wire at leas.t one inch 
from the surface wired over, and must be kept apart at least 
two and one-half inches for voltages up to 300 and four 
inches for higher voltages. 

Rigid supporting requires, under ordinary conditions, where 
wiring over flat surfaces, supports at least every four and one- 
half feet. If the wires are liable to be disturbed, the distance 
between supports should be shortened. In buildings of mill 
construction, mains of No. 8 B. & S. gage wire or over, where 
not liable to be disturbed, may be separated about six inches, 
and run from timber to timber, not breaking around, and may 
be supported at each timber only. 

In damp places the wires are often run on the under side 
of an inverted trough as shown in Figure 95. The main point 
of usefulness of such a .trough lies in the fact that it prevents 
drippings from wetting the wires and insulators. Condensa- 
tion will, however, keep insulators and wires wet neverthe- 
less. 

The trough, to be useful, should be put together with many 



162 



MODEKN ELECTRICAL CONSTRUCTION, 



screws, the butting edges of the boards having been first 
painted with a waterproof paint, with which, when finished, 
the whole trough is also painted inside and out. 

Notwithstanding the rule given above,, it would seem far 
better where practicable to use petticoat insulators and keep 
them much farther apart, even if, in order to do so, a larger 
wire would be required. Each insulator, when wet, allows 
some current to leak over its surface and, therefore, the 
fewer we have the better so long as there is no danger of 
breaking wires. If splices are necessary in wet places they 
should be made quite a distance from insulators , the insula- 
tion of a splice being always weaker than that of the unbroken 
wire. Care should also be taken that the insulation of wires 
be not damaged through tying. 

Weather-proof sockets are required by the rule and are 





Figrure 95. 



best in such places when not subject to much handling. As 
these are, however, easily broken, brass shell sockets are often 
used. These are thoroughly covered with tape and compound 
so as to exclude all moisture and are very durable. 



LOW POTENTIAL SYSTEMS. 



163 



For Moulding Work (Wooden and Metal). 

(For construction rules see No. 50. 
See also No. 25 A.) 

k. Must have an approved rubber insulating covering. 
(For wooden moulding see No. 41, for metal moulding see 
No. 47.) 

/. Must never be placed in either metal or wooden mould- 
ing in concealed or damp places or where the difference of 
potential between any two wires in the same moulding is over 
300 voLts. Metal mouldings must not be used for circuits 
requiring more than 660 watts of energy. 

As a rule, wooden moulding* should not be placed directly 
against a brick wall, as the wall is likely to "sweat" and thus 
introduce moisture back of the moulding. 

m. Must for alternating current systems if in metal 

moulding have the two or more wires of a circuit installed 

in the same moulding. 

It is advised that this be done for direct current systems 
also, so that they^ may be chang-ed to alternating systems at 
any time, induction troubles preventing such a change if the 
wires are in separate moulding-s. 

Figure 96 shows the dimensions of approved moulding. 




Figure 96. 




Figure 97. 



Figure 97 shows the proper method of making a tap joint 
in moulding. This method brings the capping between the two 



164 



MODERN ELECTRICAL CONSTRUCTION. 



wires of opposite polarity. Wires should never be crossed be- 
low the capping. If the exposed wire in Figure 97 is objec- 
tionable, part of the back of moulding may be cut out, or the 
wall back of the moulding may be gouged out as shown in Fig- 
ure 98. This method must, however, never be used with other 
than walls or partitions of hardwood. 

Figure 99 shows proper method of tapping flexible cord to 



Fig. 98. 





Figure 99. 



wires in moulding. The Vv^hole cord should never be taken 
out of one hole in capping. There is always some chance of 
abrasion and joints are often poorly covered, so that there is 
always more likelihood of short circuits at this point. 

Figure 100 shows how moulding should be fastened to tile 
ceiling. When toggle bolts are used, the nut should always be 
put on outside of capping (unless a very small one is used, or 
more than ordinary care is exercised). Many wiremen are 
careless and cut away the middle tongue too much, giving the 
nut a chance to work itself diagonally across it, so as to come 
in contact with both wires and, in time perhaps, cause short 
circuits. Although toggle bolts are mostly used, screws have 
been successfully used in tile. It is only necessary to first 
drill a hole of just the proper size for the screw to be used. 

A very rough, quick way of making a square turn with 



LOW rOTENTIAL SYSTEMS. 



165 



moulding is shown in Figure 101. One piece is cut entirely 
off along the line a; the pieces are then joined as shown and 





Fignre 101. 



Figure 102. 



the capping hides the botch work. Such work will not be 
passed by inspectors if no.ticed. The proper way of fitting 
moulding is shown in Figure 102. 

Figure 103 shows methods of running around corners. 
The saw cuts, a, b, c, etc., should be made with a fine saw and 
for short bends require to be close together. Bending is 




Figure 103. 

facilitated by wetting the moulding, and if, before the mould- 
ing is put in place, the saw cuts are filled with glue, it will 
greatly add .to the durability of the job. Screws or nails 
used in fastening the capping should pass through the mould- 
ing into the wall to get a firm hold. 



1G6 MODEKN ELECTRICAL CONSTRUCTION. 

For Conduit Work. 

n. Must have an approved rubber insulating covering (see 
No. 47). 

0. Must not be drawn in until all mechanical work on the 
building has been, as far as possible, completed. 

Conductors in vertical conduit risers must be supported 
withiu the conduit system in accordance with the following 
table :— - 

No. 14 to every 100 feet. 

No. 00 to 0000 every 80 feet. 

0000 to 350,000 C. M. every 60 feet. 

350,000 C. M. to 500,000 C. M. every 50 feet. 

500,000 C. M. to 750,000 C. M. every 40 feet. 

750,000 C. M. every 35 feet. 

A turn of 90 degrees in the conduit system will constitute 
a satisfactory support, as per above table. 

The following methods of supporting cables are recom- 
mended : — 

1. Junction boxes may be inserted in the conduit system 

at the required intervals, in which insulating sup- 
ports of approved type must be installed and se- 
cured in a satisfactory manner so as to withstand 
the weight of the conductors attached thereto, the 
boxes to be provided with proper covers. 

2. Cables may be supported in approved junction boxes 

on two or more insulating supports so placed that 
the conductors will be deflected at an angle of 
not less than 90 degrees and carried a distance of 
not less thani twice .the diameter of the cable from 
its vertical position. Cables so suspended may be 
additionally secured to these insulators by tie wires. 
Other methods, if used, must be approved by the Inspec- 
tion Department having jurisdiction. 

Figure 104 shows diflFerent methods employed to fasten 



LOW rOTEiNTIAL SYSTEMS. 



167 



wires in vertical runs in conduits. In the upper left-hand 
figure insulators are used, reinforced by metal straps so ar- 
ranged that they will prevent the insulators from being pulled 
off sideways. The method shown in the lower figure is some- 



n 




I 

pi 




t" 








h^ 


^(^ 


4. 


i, 1 

y 


M 


L./4> 




S^ 






< 


6/ T| 








^ '% 


\ 1 








S fJ 





Figure 104. 

times used with cables so heavy that the rubber insulation 
will not stand the strain of supporting them. The figure 
shows a clamp made of copper so that it can be soldered to 
the bare wires of the cable. This clamp is mounted on slate 
so as to furnish the insula.tion necessary for the cable. 

p. Must, for alternating systems, have the two or more 
wires of a circuit drawn in the same conduit. 

It is advised that this be done for direct-current systems 



1G8 MODERN ELECTRICAL CONSTRUCTION. 

also, so that they may be changed to alternating systems at 
any time, Induction troubles preventing such a change if the 
wires are in separate conduits. 

The same conduit must never contain circuits of different 
systems, but may contain two or more circuits of the same 
system. 

Tf a single wire carrying alternating currents of electricity 
were run in iron pipe there would be a very large drop in 
voltage. This drop is due to the fact that all currents while 
changing in strength generate a counter E. M. F. in their sur- 
roundings. This is particularly strong when the wires are sur- 
rounded by, or very close to, iron. If both wires are run in 
the same pipe the current in one wire neutralizes that of the 
other and there is no trouble. 

For Concealed *'Knob and Tube" Work. 

q. Must have an approved rubber insulating covering (see 
No. 41). 

r. Must be rigidly supported on non-combustible, non-ab- 
sorptive insulators which separate the wire at least one inch 
from the surface wired over. Should preferably be run singly 
on separate timbers, or studdings, and must be kept at least 
five inches apart. Must be separated from contact with the 
walls, floor timbers and partitions through which they may 
pass by non-combustible, non-absorptive insulating tubes, such 
as glass or porcelain. 

Rigid supporting requires, under ordinary conditions, where 
wiring along flat surfaces, supports at least every four and 
one-half feet. If the wires are liable to be disturbed, the 
distance between supports should be shortened. 

At distributing centers, outlets or switches where space 
is limited and the five-inch separation cannot be maintained, 
each wire must be separately encased in a continuous length 
of approved flexible tubing. 

Wires passing through timbers at the bottom of plastered 
partitions must be protected by an additional tube extending 
at least four inches above the timber. 

i". When, in a concealed knob and tube system, it is im- 
practicable to place the whole of a circuit on non-combustible 
supports of glass or porcelain, that portion of the circuit 
which cannot be so supported must be installed with Vipproved 



LOW POTENTIAL SYSTEMS. 



169 



metal conduit, or approved armored cable (see No. 24 0» ex- 
cept that if the difference of potential between the wires is 
not over 300 volts, and if the wires are not exposed to mois- 
ture, they may be fished if separately encased in approved 
flexible tubing, extending in continuous lengths^ from porce- 
lain support to porcelain support, from porcelain support to 
outlet, or from outlet to outlet. 

An illustration of wiring on the ''loop" system is shown in 
Figure 105. This system makes it unnecessary .to have any 




concealed joints or splices. The amount of wire required is 
somewhat in excess of that required for tap systems, but this 
is often balanced by a saving in labor. Sometimes, however, 
the labor is also in excess of that required for tap systems. 



170 MODERN ELECTRICAL CONSTRUCTION. 

The main advantage of the system is that all joints and splices 
are always accessible. The figure also shows mixed *'knob 
and tube" work and '*conduit" work. Along the walls behind 
the furring strips there is seldom sufficient space to admit of 
knob and tube work and conduit must be used. 

t. Mixed concealed knob and tube work is provided for 
in No. 24 s, must comply with requirements of No. 24 n .to p, 
and No. 25, when conduit is used, and with requirements of 
No. 24 A, when armored cable is used. 

u. Must at all outlets, except where conduit is used, be 
protected by approved flexible insulating tubing, extending in 
continuous lengths from the last porcelain support to at least 
one inch beyond the outlet. In the case of combination fix- 
tures the tubes must extend at least flush with outer end of 
gas cap. 

It is recommended, but not required, that approved outlet 
boxes or plates be installed at all outlets in concealed "knob 
and tube" wOrk, the wires to be protected by approved flexible 
insulating- tubing-, extending in continuous lengths from the 
last porcelain support into the box. 

Figure 106 is drawn to illustrate "fish work." Fish work is 
used in finished buildings, mostly, and is often very tedious 
and expensive. Hours are sometimes spent before wires can 
be brought throu9^h and often the effort ^'s an entire failure. 
In combination work, as shown in Figure 91, there is usually 
little trouble, as there is the whole sp:in between joists to run 
wires in. An effort to fish at right angles to the joists (when 
there are s^-rips under joists) is more difficult, but often suc- 
cessful if the distaiice is not too great 

When ihcre are two men the usual method of fishing is: 
One man takes a wire sufficiently long to reach from one open- 
ing .to the other, and, after bending a small hook on one end 
in such a way that it will not catch easily on obstructions, 
pushes this end into one opening and, by twisting and working 
backward and forward, gradually forces it toward the other 



LOW POTENTIAL SYSTEiMS. 



171 



opening. At this opening his helper is stationed with a short 
wire, also provided with a hook, with which he must seek to 
catch the other wire when it comes near his opening. When 
the two wires come in contact, the larger one is drawn out and 
the conducting wires (encased in approved flexible tubing) 
are fastened to it and drawn through. The tubing should 
always be put on the wires before drawing in. If it is put on 







Figure 106. 

later there is much temptation to leave it as indicated at the 
right of the figure at a. This trick is quite common, but is 
very easily detected by inspectors ; the wire at either end can 
easily be pushed in without pushing out at the other, as it 
would if the tubing were continuous. If the tubing has been 
taped to the wires this will be impossible, but either one of the 
tubings can still be moved without moving the other, which 
would be impossible in a job properly done. The tubing must 
consist of one piece, and there must be only one wire in each 
tubing 

If one man is alone on a fish job, a handful of small wire 



172 MODERN ELECTRICAL CONSTRUCTION. 

is pushed into one opening in a manner which will allow it 
to spread out considerably. When the fish wire from the 
other opening comes in contact with it, it will indicate it by 
moving this wire, which can be seen by that left hanging out. 
A small fish wire is then used to draw out the long one. If 
the two openings are in different rooms and not visible, one 
from the other, a bell and battery can be used, as shown in 
the drawing, if there are no wire lath. 

When wires are to be entirely concealed it is nearly always 
necessary to find a way through headers, timbers, etc. ; this 
can hardly be done without cutting holes in plaster. A method 
doing as little damage as any is shown at the top in Figure 106. 
A hole is bored through the 2X4, which will allow the wire, 
when job is finished, to continue downward as shown by dotted 
lines, 1 and 2. Such turns are seldom ever used with electric 
light wires on account of their size ; they are more practicable 
with bell or telephone wires. 

Where it is desired to keep wires from showing in a parlor, 
for instance, they can be fished from an adjoining room, as 
indicated by dotted line 3, where the wires are run down 
partition in moulding in closet and then through to switch, 
which is in the same room with the lights. Before under- 
taking a job of fish work it is well to look the whole building 
over carefully. There are often false walls along chimneys, 
especially at both sides of mantels, in which wires can be 
easily run from basement to attic. 

Often it may be necessary to remove baseboards in order 
to find room for wires. When removing such boards never 
attempt to drive nails out, always break them off; if driven 
out they will usually split off parts of the board. 

Soft wood floors can easily be taken up when necessary. 
Use a broad thin chisel and cut away the tongue on each side 
of the board to be taken up; the board can then be readily 



LOW POTENTIAL SYSTEMS. 173 

taken up. With double floors or with tightly laid hardwood 
floors, it is better to cut pockets in ceiling below. 

For Fixture Work. 

V. Must have an approved rubber insulating covering (see 
No. 46) and be not less in size than Xo. 18 B. & S. gage. 

See No. 46, e, fine print note, for exceptions to the use of 
rubber-covered wire. 

w. Supply conductors, and especially the splices to fixture 
wires, must be kept clear of the grounded part of gas pipes, 
and, where shells or outlet boxes are used, they must be made 
sufficiently large to allow the fulfillment of this requirement. 

.r. Must, when fixtures are wired outside, be so secured 
as not to be cut or abraded by the pressure of the fastenings 
or motion of the fixture. 

y. Under no circumstances must there be a difference of 
potential of more than 300 volts between wires contained in or 
attached to the same fixture. 

24 A. Armored Cables. 

{For construction rules, see No. 48.) 

a. Must be continuous from outlet to outlet or to junction 
boxes, and the armor of the cable must properly enter and be 
secured to all fittings, and the entire system must be me- 
chanically secured in position. 

In case of underground service connections and main runs, 
this involves running- such armored cable continuously into a 
main cut-out cabinet or gutter surrounding the panel board, as 
the case may be. (See No. 54.) 

b. Must be equipped at every outlet with an approved out- 
let box or plate, as required in conduit work. (See Xo. 49A.) 

Outlet plates must not be used where it is practicable 
to install outlet boxes. 

The outlet box or plate shall be so installed that it wili 
be flush with the finished surface, and if this surface ii; 
broken it shall be repaired so that it will not show any gaps 
or open spaces around the edge of the outlet box or plate. 

In buildings already constructed where the conditions are 
such that neither outlet box nor plate can be installed, these 
appliances may be omitted by special permission of the Inspec- 



174 MODERN ELECTRICAL CONSTRUCTION. 

tion Department having jurisdiction, provided the armored 
cable is firmly and rigidly secured in place. 

c. Mus.t have the metal armor of the cable permanently 

and effectively grounded. 

It is essential that the metal armor of such systems be 
joined so as to afford electrical conductivity sufllcient to 
allov^^ the largest fuse or circuit breaker in the circuit to 
operate before a dangerous rise in temperature in the system 
can occur. Armor of cables and gas pipes must be securely 
fastened in metal outlet boxes so as to secure good electrical 
connection. Where boxes used for centers of distribution do 
not afford good electrical connection, the armor of the cables 
must be joined around them by suitable bond wires. Where 
sections of armored cable are installed v^^ithout being fastened 
to the metal structure of building or grounded metal piping, 
they must be bonded together and joined to a permanent and 
eflacient ground connection. 

d. When installed in so-called fireproof buildings in course 
of construction or afterwards if concealed, or where it is ex- 
posed to the weather, or in damp places such as breweries, 
stables, etc., the cable must have a lead covering at least 1/32 
of an inch in thickness placed between the outer braid of the 
conductors and the steel armor. 

e. Where entering junction boxes and at all other outlets, 
etc., must be provided with approved terminal fittings which 
will protect the insulation of the conductors from abrasion, 
unless such junction or outlet boxes are specially designed and 
approved for use with the cable. 

/. Junction boxes must always be installed in such a man- 
ner as to be accessible. 

g. For alternating current systems must have the two or 
more conductors of the cable enclosed in one metal armor. 

25. Interior Conduits. 

(See also Nos. 24 n to p, and 4Q.) 

The object of a tube or conduit is to facilitate the insertion 
or extraction of the conductors and to protect them from me- 
chanical injury. Tubes or conduits are to be considered 
merely as raceways, and are not to be relied upon for in- 
sulation between wire and wire or between the wire and the 
ground. 

The installation of wires in conduit not only affords the 



LOW POTENTIAL SYSTEMS. 175 

wires protection from mechanical injury, but also reduces the 
liability of a short circuit or ground on the wires producing 
an arc, which would set fire to the surrounding material ; the 
conduit being generally of sufficient thickness to blow a fuse 
before the arc can burn through .the metal of the pipe. For 
this reason the wires should be entirely encased in metal 
throughout, both in the conduit and at all outlets. Another 
advantage derived from the use of iron conduit is the facility 
wMth which wares can be ex.tracted and replaced in case a 
fault develops on any of them. The saving which this may 
mean in cases where the installation of new wires would 
necessitate the destruction of costly decorations can readily be 
seen. It must be remembered that the arc or burn produced 
by a short circuit or ground is proportional to the size of the 
fuse protecting the circuit. If a large fuse, say 30 amperes, is 
used to protect a branch circuit and a ground or short occurs 
on this circuit, the wire may become fused to the pipe so that 
it cannot easily be pulled out. This is one reason why fuses 
should be as small as practicable. More than six amperes is 
seldom used on branch circuits, so that no larger fuse than 
this should ordinarily be used. The installation of wires in 
iron conduit also reduces the liability of lightning discharges 
entering a building as the pipe surrounding the wires offers 
great resistance to the passage of these sudden currents. 

Conduit is classed under .two general heads, lined and un- 
lined. In both classes of conduit the same thickness of metal 
is required. 

a. No conduit tube having an internal diameter of less 
than five-eighths of an inch shall be used. Measurements to 
be taken inside of metal conduits. 

This rule favors lined conduit insomuch that it requires 
the same pipe for lined and unlined, and allows a lined con- 
duit of less than five-eighths of an inch in diameter. 



176 



MODERN ELECTRICAL CONSTRUCTION. 



b. Must be .continuous from outlet to outlet or to junc- 
tion boxes, and the conduit must properly enter, and be secured 
to all fittings and the entire system must be mechanically se- 
cured in position. 

In case of service connections and main runs, this involves 
running- each conduit continuously into a main cut-out cabinet 
or gutter surrounding the panel board, as the case may be 
(see No, 54). 

When conduit is used every run of pipe must end in acces- 
sible outlet boxes. This box may be a cut-out center, switch 
outlet, fixture outlet or a junction box. If a mixed form of 
wiring is used, where part of a circuit is run in conduit and 
the balance with some other form of construction, such as 




K 



1^ 



"•— JuY>ct\on box 



£<^«-. 



.,--\0tK AAUX 




P> 



Figure 107. 



concealed knob and tube work, for instance, the conduit must 
in all cases enter the box and be firmly attached to it, as 
shown in Figure 107. Cases are sometimes found where the 



LOW POTENTIAL SYSTEMS. 



177 



conduit is broiiglit just to the l)ox, Ijut docs not enter it, the 
wires being extended through holes into the box. This method 
of wiring is obviously wrong, as a wireman is apt to find if 
he ever has occasion to replace wires in such a system. The 
same holds true of cut-out centers. Here also every run of 
conduit must enter the box. The conduit should not simply 
be brought to the sides or the back of the cut-out center and 
the wires then carried to the cut-outs in flexible tubing, but 
everv conduit should enter clear into the box so that when 




Figure 108. 



the work is completed there will be no exposed wiring. In 
the case of main runs the conduit should enter the boxes and 
never be broken between the outlets. Sometimes it is neces- 
sary to install meters on the mains and the conduit is ended 
and the wires carried to the meters and then either ex.tended 



178 MODERN ELECTRICAL CONSTRUCTION. 

in conduit or carried into the cut-out center. This construc- 
tion should be avoided. If a meter is to be installed near a 
cut-out center, the main conduit should be carried into the box 
and the necessary meter loops then brought out. In this way 
the quantity of wire outside of conduits is reduced to a mini- 
m.um. If a meter is to be installed in some location along the 
mains other than at the cut-out center or service switch, a 
junction box should be provided and the meter loops brought 
out from that. This is shown in Figure 108, which also 
shows a cut-out box as used with conduit systems. 

c. Must be first installed as a complete conduit system, 
without the conductors. 

As fast as the conduit is installed, the ends of the pipes 

should be closed, using paper or corks. This does away with 

the liability of plaster or other substances entering the pipes 

and causing trouble when the wires are to be pulled in. The 

conductors should not be pulled in until all the mechanical 

work on the building is, as far as possible, finished. When a 

conduit system is ready for the wires, the "pulling in" may be 

done in various ways. For short runs, all that is necessary is 

to shove the wires in at one opening until they come out at 

the other. If a run is too long to be inserted in this way, 

what is known as a "fish wire" can be used. The ordinary 

fish wire is a flat band of s.teel about 5/32 inch wide and 1/32 

inch thick. This wire can be forced through any ordinary 

length of pipe. Ordinary round steel wire of about No. 12 

or 14 B. & S. gage can also be used, although this is not as 

good as the fish wire above described. 

« 
The end of the wire is first bent back so as to form a very 

small hook or eye ; this will enable it to slide easily over ob- 
structions in the pipe and also make it possible should it stick 
somewhere to engage it with another fish wire provided with 



LOW POTENTIAL SYSTEMS. 179 

a suitable hook and entered from the other end of the pipe. 
This is very often necessary in runs having many bends. The 
fish wire, having been pushed through the pipe, is now fastened 
to the copper wire by means of a strong hook and the copper 
wire pulled into the pipe. 

In pulling in the large size cables, it is often found advan- 
tageous to pull on the fish wire and at the same time push on 
the end of the cable entering the pipes. It is also well to 
remember that it is easier to pull down than to pull up, as, 
when pulling down, .the weight of the cable assists. The use 
of soapstone facilitates the drawing in of the wires. The wire 
may either be covered with the powdered soapstone or the 
soapstone may be blown into the pipes. An elbow partly 
filled with soapstone is often found convenient for blowing the 
soapstone into .the pipe, ahvays blowing from the highest point. 

Graphite or axle grease should never be used for this 
purpose, as the graphite is a conductor and the axle grease 
will rot the rubber insulating covering of the wire. 

d. Must be equipped at every outlet with an approved out- 
let box or plate (see No. 49 A). 

Outlet plates must not be used where it is practicable to 
install outlet boxes. 

The outlet box or plate shall be so Installed that it will 
be flush with the finished surface, and if this surface is 
broken it shall be repaired so that it will not show any gaps 
or open spaces around the edge of the outlet box or plate. 

In buildings already constructed where the conditions are 
such that neither outlet box nor plate can be installed, these 
appliances may be omitted by special permission of the Inspec- 
tion Department having jurisdiction, provided the conduit ends 
are bushed and secured. 

' The object of an outlet box is to hold the conduits firmly 
in place, to connect the various runs of conduit so that they 
form a continuous electrical path to the ground, and to afford 
a fireproof enclosure for the joints, switches, etc Outlet 



180 MODERN ELECTRICAL CONSTRUCTION. 

boxes are made in various designs to meet the requirements 
of the work on which they are .to be used. 

Where it is impossible to use an outlet box, an outlet plate 
can be used. These plates are fitted with set screws so that 
they hold the ends of the conduits firmly in position and make 
the metal of the system continuous. They do not afford a 
fireproof enclosure for the joints and for that reason should 
never be used when it is practicable to use an outlet box. If 
the conditions are such that neither an outlet box nor plate can 
be used, special permission can be obtained from the Inspec- 
tion Department having jurisdiction to omit them. In this 
case the conduits should be bushed at the ends and the pipes 
should be bonded together. 

e. Metal conduits where they enter junction boxes, and at 
all other outlets, etc., must be provided with approved bush- 
ings, fitted so as to protect wire from abrasion, except when 
such protection is obtained by the use of approved nipples, 
properly fitted in boxes or devices. 

When a piece of conduit is cut with a pipe cutter, a sharp 
edge is left on the inside. This edge, if left on, would soon 
cut into the insulation of the wires. It should be removed by 
means of a pipe reamer. The bushing can now be screwed on 
as shown in Figure 107, a locknut having firs.t been screwed 
onto the pipe. The locknut and bushing are then screwed up 
so that they are tight and form a good connection. 

f. Must have the metal of the conduit permanently and 
effectually grounded. 

It is essential that the metal of conduit systems be joined 
so as to afford electrical conductivity sufficient to allow the 
largest fuse or circuit breaker in the circuit to operate before 
a dang-eroiis rise in temperature in the conduit system can 
occur. Conduits and g"as pipes must be securely fastened in 
metal outlet boxes so as to secure g-ood electrical connection. 
Where boxes used for centers of distribution do not afford 
g-ood electrical connections, the conduits must be joined 
around them by suitable bond wires. Where sections of metal 



LOW POTENTIAL SYSTEMS. 181 

conduit are installed without being- fastened to the metal struc- 
ture of buildings or grounded metal piping they must be 
bonded together and joined to a permanent and efficient ground 
connection. 

That the metal in a conduit system should be peftt1?l'nently 
and effectually grounded is plainly evident when the hazards 
which are present with ungrounded or poorly grounded con- 
duit are recalled. Until recently very little attention has 
been given to the matter of properly grounding conduits, but 
with the increased use the necessity of so doing has become 
very apparent. If the bare wire of one side of a system comes 
in contact electrically with the iron pipe and if there is a 
ground on the other side of the sys.tem (and there always is 
with 3-wire systems) the conduit becomes a conductor. If 
the conduit system is so installed that every piece is in good 
electrical connection and the entire system effectually grounded 
no harm will be done except the blowing of a fuse. Conduit is 
installed in all kinds of locations. It may be in contact with a 
gas pipe, lead pipe, or run in a damp floor, or it may be run 
exposed where a person could easily come in contact with it. 
The effects that might result from a conduit so run should the 
conduit become alive are readily seen. Suppose .that in the 
first case the conduit crosses the gas pipe at right angles, the 
area of contact would be very small and the effect of the cur- 
rent in a livened conduit crossing this poor contact would 
result in burning a hole in the gas pipe and igniting the escap- 
ing gas. Again, suppose the conduit run in a damp floor 
should become alive ; the damp w^oodwork, being a conductor, 
would soon char and the charred part would then readily 
ignite. 

With a system which is grounded, an exposed piece of 
conduit will usually only be alive for a very short time 
during the blowing of the fuse. Even if it remains periua- 
nently alive, current will no.t flow from it to the surrounding 



i82 MODERN ELECTRICAL CONSTRUCTION. 

material, but will take the easiest path to ground, which is 
along the conduit. On the ordinary branch circuits, the vari- 
ous runs of conduit are bonded together through the outlet 
boxes and, in connecting the condmts to these boxes, care must 
be taken that they make good contact. In order to do this, the 
conduit should enter at right angles to the Idox and the enamel 
should be scraped away from the box so that the locknut and 
bushing make good electrical connection. The same thing 
should be done where the conduit enters the cut-out box. The 
metal of the cut-out box will bond together the various branch 
conduits and the main conduit. The main conduit should now 
be connected to some good ground, such as a w^ater or steam 
pipe or metal work of the building. Never carry the ground 
wire to a gas pipe. The various branch conduits should also 
be grounded wherever possible, at and on metal beams over 
which they cross and at every gas outlet. The reason of 
grounding the gas pipe thoroughly at the gas outlets is to be 
sure of a good ground. The gas pipe is necessarily in contact 
with the outlet box at this point and any poor contact which 
might cause arcing must be avoided. 

Strictly speaking, a conduit should be grounded with a wnre 
equal to that used iii the conduit. This can easily be done in 
the case of smaller circuits, but with the larger size mains it is 
a more difficult matter. Special devices for attaching the 
ground wire to both conduit and the grounded pipes are now 
on the market and should be used. When these are not ob- 
tainable a ground connection can be made bv taking a number 
of good turns around the conduit and then soldering the 
wire to the conduit and taping the joint. A better way w^ould 
be to use a few T couplings on the system and to screw brass 
plugs to these and solder the ground wire to the plugs. Such 



LOW POTENTIAL SYSTEMS. 183 

coupiings should be installed near outlets where they will not 
intefefere much with ''fishing." 

If the ground wire has to be run for any great distance, 
it should be installed as though it were at all times alive, and 
should be kept away from inflammable material. The method 
advised under 13 A for grounding wires should be used. 
Where a 3-wire system is used^ the best ground obtainable is 
the neutral wire of .the system. When a ground is made to 
the neutral wire, it should be made back of the fuses on the 
service switch ; never make the connection with the neutral 
inside of the service switch. 

g. Junction boxes must always be installed in such a 
manner as to be accessible. 

h. All elbows or bends mus.t be so made that the con- 
duit or lining of same will not be injured. The radius of the 
curve of the inner edge of any elbow not to be less than three 
and one-half inches. Must have not more than the equivalent 
of four quarter bends from outlet to outlet, .the bends at the 
outlets not being counted. 

If more than four quarter bends are necessary, a junction 
box should be installed and the wires first pulled from one 
of the outlets .to the junction box and then from the junction 
box to the other outlet. 

Several methods are in use for bending conduit. With the 
lined conduit elbows and bends of various shapes can be 
obtained already bent, and it is much more satisfactory to use 
these, as considerable care must be exercised in making bends 
in order to keep the inside lining from coming loose from the 
pipe and causing trouble when "pulling in." To prevent this 
a suitable spiral spring is sometimes inserted into the con- 
duit before bending. Plumbers working with lead pipe often 
use coarse sand to fill the pipe before bending. This is more 
particularly useful with special conduits such as brass tubing, 



184 



MODEliN ELECTKICAL CONSTliUCTION. 



which is sometimes used in showcase or window work and 
classed with fixtures. 

With unlined conduits .the bending is a simple matter, 
although here also care must be taken to see that the conduit 
does not bend flat. In a good bend the pipe retains its circular 
form throughout the bend, w^hile, if the bend is poorly made, 
the pipe will assume an oval shape, flattening somewhat at 
the bend. The smaller size conduits can be bent in a common 
vise. This is best accomplished by gripping the pipe in the 





jsa 



Figure 109. 



vise and making a small bend, then moving the pipe for a slight 
distance and bending again, and continuing until the desired 
shape is obtained. Another method which can be used on 
small pipes is shown at a in Figure 109, using a three or four 
foot length of gas pipe or conduit w^ith an ordinary gas pipe T 
on the end. This is run over the conduit and gives sufficient 
leverage to make any bend. 

A simple device used for bending conduits is shown at 
b in Figure 109. This is constructed of metal, the wheel being 
grooved to fit the pipe. A similar device minus the wheel 
and lever may be made up of two blocks of wood firmly 
fastened to a work bench. The pipe can be bent around this 
by hand. 

For .the larger size conduits, elbows can be obtained already 



LOW I'OTENTIAL SYSTEMS. 



185 



bent. Connections between the various lengths of concUiit are 
made with the ordinary gas-pipe couplings. When the conduit 
conies from the factory each length of pipe is provided with a 
coupling at one end. (This practice is now being discon- 
tinued, the couplings being left off.) This coupling should be 
removed and the end of the conduit reamed out. The reaming 
should always be done so that there is considerable metal left 
at the end of the pipe, and it should never be carried so far as 
to leave only a sharp edge. If a thread is to be cut, it is good 
practice to take a couple of turns with the reamer after this 
has been done. The coupling can then be screwed on. When 
making the connection, the pipes should be screwed into the 
coupling so .that the ends just "butt." Do not attempt to screw 
them too tight, or, in all probability, the thread on the end 





Figure 110. 

of the pipe will be turned in and close the opening. Figure 
110, a, shows how a connection should be made. If lined con- 
duit is not properly reamed and is screwed too tight the 
opening is often entirely closed or forced inward, as shown 
at b. 

It is often necessary, especially in making changes in old 
installations, to fit pieces between two pipes, neither one of 
which can be turned so as to draw them together. In such 
cases a long thread is cut on one piece of the pipe and the 
coupling run back on it ; when the pipes are butted together 
the coupling is rnr over the two pipes, thus connecting them. 
A locknut may be run upon either pipe and used to keep the 
coupling in place. 

In running conduits avoid as much as possible passing 



186 MODERN ELECTRICAL CONSTRUCTION. 

throuj^'h bath-rooms and other places where pkimbers are 
likely to run their piping. 

When practicable, conduits shouJd be run so they will 
drain ; for instance, where crossing a room from one side 
bracket to another, it is better to run along ceiling than along 
the floor. Conduits will sometimes become quite moist inside 
from condensation. Where there is any likehhood of this 
the ends may be sealed. 

25 A. Metal Mouldings. 

(See also Nos. 24 k to m, and 50.) 

a. Must be continuous from outlet to outlet, to junction 
boxes, or approved fittings designed especially for use with 
metal mouldings, and must at all outlets be provided with ap- 
proved terminal fittings which will protect the insulation of 
conductors from abrasion, unless such protection is afforded 
by the construction of the boxes or fittings. 

h. Such moulding where passing through a floor must be 
carried through an iron pipe extending from the ceiling be- 
low to a point five feet above the floor, w^hich will serve as an 
additional mechanical prbtection and exclude the presence of 
moisture often prevalent in such locations. 

In residences, office buildings and similar locations where 
appearance is an essential feature, and where the mechanical 
strength of the moulding" itself is adequate, this ruling may 
be modified to require! the protecting piping from the ceiling 
below to a point at least three inches above the flooring. 

r. Backing must be secured in position by screws or bolts, 
the heads of which must be flush with the metal. 

d. ^ The metal of the moulding must be permanently and 
effectively grounded, and must be so installed that adjacent 
lengths of moulding will be mechanically and electrically se- 
cured at all points. 

Tt is essential that the metal of such systems be joined so 
as to afford electric conductivity sufficient to allow the largest 
fuse in the circuit to operate before a dangerous rise of 
temperature in the system ran occur. Mouldings and gas 
pipes must bo securely fastened in metal outlet boxes, so as 
to secure good electrical connection. Where boxes used for 



LOW POTENTIAL SYSTEMS. 



187 



center of distribution do not afford good electrical connection 
the metal moulding- must be joined around them by suitable 
bond wires. Where sections are installed without being 
fastened to the metal structure of the building or grounded 
metal piping they must be bonded together or joined to a 
permanent and effective ground connection. 

c. Must be installed so that for alternating systems the 
two or more wires of a circuit will be in the same metal 
moulding. 

It is advised that this be done for direct systems also, so 
that they may be changed . to the alternating system at any 
time, induction troubles preventing such change if the wires 
must be in separate mouldings. 

26. Fixtures. 

(See also Nos. 22 c, 24 v to y.) 

a. Must when supported from the gas piping or an}- 
grounded metal work of a building be insulated from such 
piping or metal work by m.eans of approz'cd insulating joints 
(see No. 59) placed as close as possible to the ceiling or walls. 

Gas outlet pipes must be protected above the insulating 
joint by approved insulating tubing, and where outlet tubes 
are used they must be of sufficient length to extend below 
the insulating joint, and must be so secured that they will not 
be pushed back when the canopy is put in place. 

Where canopies are placed against plaster walls or ceilings 
in fireproof buildings, or against metal walls or ceilings, or 
plaster walls or ceilings on metallic lathing in any class of 
buildings, they must be thoroughly and permanently insulated 
from such walls or ceilings. 

Figure 111 shows insulating joints such as are used to insu- 
late fixtures from the gas piping of buildings. 

The object of an insulating joint is to prevent a "ground" 
on one fixture from causing trouble on other fixtures. If, for 
instance, one fixture in a building were in contact with the 
positive wire of the system and another in contact with a 
negative wire, and the two fixtures connected direct to the gas 
piping, the two contacts or "grounds'' would form a short cir- 
cuit, the current flowing from one pole along the gas piping to 
the other. This becomes impossible when the fixtures are 



188 



MODEKN ELECTRICAL CONSTKUCTION. 



insulated from the piping, or conducting parts of ceilings. 

Insulating joints are made in a variety of patterns. The 
one shown at a in Figure 111 is designed for use on a com- 
bination gas and electric fixture, and is made to allow the gas 






Figure 111. 

to pass through. Other forms, such as b, can be used on con- 
duit work to connect to the stub in the outlet box, or on a gas 
outlet where it is desired to use the electric light only. 

Insulating joints should be placed as close as possible to the 
ceiling, so that there will be a minimum of exposed pipe above 




Figure 112. 

the joint. If the gas pipe has been left long so that the' insu- 
lating joint comes some distance below the ceiling, it is a good 
plan to pro.tect the pipe above the joint either by using a porce- 
lain tube which will fit over the pipe or by taping the pipe 



LOW POTENTIAL SYSTEMS. 



189 



thoroughly. Flexible tubing is also sometimes used. See 
Figure 112. 

In conneeting the fixture, eare should be taken that the 
extra wire usually left for making the joiat is twisted around 
the pipe below the insulating joint; never above. If the wires 
at the outlet have beeen properly run, as shown in Figure 112, 
the flexible tubing will extend to the bottom of .the insulating 
joint. 

When a straight electric fixture is to be installed on some 
grounded part of the building, a crowfoot, shown at c, Figure 
111, can be fastened to the metal work and the fixture then 
connected wi.th the insulating joint. 

If the fixture is to De mounted on plaster, a hardwood 
block can be screwed to the wall or ceiling and a crowfoot 
screwed to this. The screws holding the crowfoot must no.t 
extend through the block. Such a case is illustrated at the 
right in Figure 112. 

Before the plastering is put on, a board should be fastened 




Figure 113. 



between the jois.ts, so that the wooden block may later be 
screwed to it. This is not absolutely necessary, as screws in 
lath will usually hold light fixtures. Heavy fixtures in old 
buildings can best be hung as shown at h, in Figure 113. This 



190 MODERN ELECTRICAL CONSTRUCTION. 

method is also used for ceiling fan motors. These motors 
must never be rigidly fastened, but should always be left free 
to swing and find their own centers. 

In connection with open or moulding work, the canopies 
should always be cut out, so that the loom or moulding may 
enter them. On no account should wires be allowed to rest 
on sharp edge of canopy. See a, Figure 113. 

Figure 113 illustrates at c how fixtures are fastened to tile 
ceilings, toggle bolts and a metal strip to which a piece of pipe 
is fastened being used. 

Fiber is often used for the insulation of canopies from the 
ceiling. Figure 113 at d shows a bug insulator, which can be 
used for this purpose. A hole is drilled in the center of a 
small block of fiber, and it is then slotted lengthwise with a 
saw. A small dent is made in the upper edge of the canopy 
and the fiber block slipped on the edge, so that the small dent 
fits into the hole. If a hole is punched through the edge of 
the canopy, and a brass pin riveted in, a much better job is 
obtained. Short, thin strips of fiber, or a long strip riveted to 
the inside of the canopy and left to project about one-eighth 
inch, are often used. These being placed on the inside of the 
canopy are much more sightly than the bug insulators. When 
a wooden block is used to fasten the fixture to the wall, the 
block may be made large enough so that the canopy will fit 
p.gainst it. The practice of fastening the canopy a short dis- 
tance from the ceiling does not comply with the rule. 

b. Must have all burs, or fins, removed before the con- 
ductors are drawn into the fixture. 

c. Must be tested fbr "contacts," between conductors and 
fixture, for "short circuits" and for ground connections before 
it is connected to its supply conductors. 

Fixtures are always made up of gas piping and their con- 
struction is, therefore, very similar to conduit work. 



LOW rOTEXTIAL SYSTEMS. 101 

Three tests should be made on each fixture before it is con- 
nected. If tests are not made until fixtures have been con- 
nected, it is often necessary to disconnect them again to de- 
termine whether a fault is in the fixture or in the wiring. 
Where there are several fixtures on one circuit and a short 
circuit should be discovered, it would also likely be necessary 
to disconnect several of them before the right one would be 
found. 

A test for short circuit may be made, first, by connecting 
the two wires of a magneto to the two main wires at top of 
fixtures. If all sockets are properly connected and the wiring 
is clear, no ring will be obtained. If a ring is obtained, it 
indicates a short circuit. 

Without changing connections each socket may now be 
tested for connections. While one man is operating the mag 
neto, another may insert a screw-driver, jack-knife, or piece oi 
wire into each socket in turn, thus connecting the two termi- 
nals and causing a ring of the magneto. Failure to obtain a 
ring would indicate an open circuit, which must, of course, be 
remedied. 

The third test is made for ^'grounds." To make it, the two 
fixture wires are connected to one wire of the magneto and 
the other wire is connected to the metal of .the fixture. 

It is best to connect this wire to the iron piping, and not to 
the lacquered brass ; the lacquer is often a very good insulator. 
If a ring is now obtained, it indicates that the insulation on a 
wire has been damaged, and that the bare wire is in contact 
with the fixture. This test can be made more thorough by 
working the accessible fixture wires back and forth during the 
test; sometimes a damaged portion of wire is not in contact 
with the metal of fixture while lying upon the floor, but may be 
brought in contact with it when hanging. 

Fixtures that have been connected to the circuit and pro 



192 



MODERN ELECTRICAL CONSTRUCTION. 



vided with insulating joints can be individually tested for 
''grounds," by connecting one wire of a magneto to the body 
of the fixture and the other, first to one, and then the other, 
of the circuit wires in the sockets. This test wall detect a 
"ground" in a fixture without disconnecting it from the cir- 
cuit. 

In connecting sockets to fixtures, it is advisable to connect 
them so that all protruding parts, as keys or receptacles for 
lamps, be of the same polarity, that is, all connected to the 
same main wire. This also applies to reflectors, border lights 
for theaters, encased in metal, etc. This will not lessen the 
liability of such parts to "ground," but lessens the chances 
of short circuits very much. Many "shorts" are brought about 
by the projecting brass lamp butts on fixtures being of opposite 
polarity. If they are of the same polarity, they will cause no 
trouble. 

Special fix,tures for show windows, etc., are often made up 
as shown in Figure 114. The construction shown at the left is 




Figure 114. 



more compact and neat, but requires more care in installing 
than the other, because of the edges of pipe in contact with 
the wires. If very long fixtures of this kind are installed, it is 



LOW POTENTIAL SYSTEMS. 193 

advisable to insert insulating joints as often as practicable, 
even if necessary to run wires around them. 

d. All fixture arms made of tubing smaller than J^ inch 
outside diameter, also the arms of all one-light brackets, 
must be secured after .they are screwed into position by the 
use of a set-screw properly placed, or by soldering or cement- 
ing or some equally good method to prevent the arms from 
becoming unscrewed. Arms must not be made of tubing 
lighter than No. 18 B. & S. gage, and must have at screw 
joints not less than five threads all engaging. This rule does 
not apply to fixtures or brackets with cast or heavy arms. 

27. Sockets. 

(For construction rules, see No. 33.) 

a. In rooms where inflammable gases may exist the incan- 
descent lamp and socket must be enclosed in a vapor-tight 
globe, and supported on a pipe-hanger, wired with approved 
rubber-covered wire (see No. 41) soldered directly to the 
circuit. 

Ke^ sockets contain a switch (see No. 17 &). 

In Figure 115, a shows a "vapor-tight" globe suspended on 
a pipe hanger, the construction of which complies with the 
requirements of this rule. If moisture is present it is well to 
seal the upper end of the pipe with compound. 

Key sockets must not be used in rooms where inflammable 
gases exist. If enclosed as required above they would be 
useless. 

b. In damp or wet places "waterproof" sockets must be 
used. Unless made up on fixtures they must be hung by 
separate stranded rubber-covered wires not smaller than No. 
14 B. & S. gage, which should preferably be twisted together 
when the pendant is over three feet long. 

These wires must be soldered direct to the circuit wires 
but supported independently of them. 

c. Key sockets will not be approved if installed over spe- 



194 



MODERN ELECTRICAL CONSTRUCTION 



cially inflammable stuff, or where exposed to flyings of com- 
bustible material. 

Waterproof sockets are constructed entirely of porcelain 
and are not provided with keys, therefore the circuits .to which 
they are connected must be controlled by switches. As a gen- 
eral rule these sockets are furnished with a short piece of 




Figrure 115. 



stranded, rubber-covered wire extending through sealed holes 
in the top of the socket and the supporting wires are soldered 
to them. The method of suspending waterproof sockets varies 
with the conditions. Ordinarily, stranded rubber-covered 
wires of the proper length are suspended from single cleats as 
shown at b, in Figure 115, or, if the line knobs are large 
enough, the stranded wire may be supported from .them. If 
the lamp is to be suspended only a short distance from the 
ceiling, where it will not be liable to be disturbed, it may be 



LOW POTENTIAL SYSTEMS. 195 

hung from two ordinary inch porcelain knobs, as shown in 
Figure 95. If cleats are used in a damp place for supporting 
the drop a half cleat must be provided back of the supporting 
cleat to give a one-inch separation, as required for wires in 
wet places. 

28. Flexible Cord. 

a. Must have an approved insulation and covering (see 
No. 45). 

h. Must not be used where the difference of potential 
between the two wires is over 300 volts. 

The above rule does not apply to the grounded circuits in 
street railway property. 

c. Must no.t be used as a support for clusters. 

d. Must not be used except for pendants, wiring of fix- 
tures, portable lamps or motors, and portable heating ap- 
paratus. 

The practice of making the pendants unnecessarily long and 
then looping them up with cord adjusters is strongly advised 
against. It offers a temptation to carry about lamps which are 
intended to hang freely in the air, and the cord adjusters wear 
off the insulation very rapidly. 

For all portable work, including those pendants which are 
liable to be moved about sufficiently to come in contact with 
surrounding objects, flexible wires and cables especially de- 
signed to withstand this severe service are on the market, and 
should be used. (See No. 45 f.) 

The standard socket is threaded for one-eighth-inch pipe, 
and if it is properly bushed the reinforced flexible cord will 
not g-o into it, but this style of cord may be used with sockets 
threaded for three-eighths-inch pipe, and provided with sub- 
stantial insulating- bushings. The cable to be supported inde- 
pendently of the overhead circuit by a single cleat, and the two 
conductors then separated and soldered to the overhead wires. 

The bulb of an incandescent lamp frequently becomes hot 
enough to ignite paper, cotton and similar readily ignitible 
materials, and in order to prevent it from coming in contact 
with such materials, as well as to protect it from breakage, 
every portable lamp should be surrounded with a substantial 
wire guard. 

Cord adjusters should never be used where their use can 
be avoided and where they are installed should only be placed 



196 MODERN ELECTRICAL CONSTRUCTION. 

on lamps which will seldom need adjusting. The indis- 
criminate use of cord adjusters cannot be too strongly con- 
demned, as the constant rubbing soon destroys the insulation. 
At c, Figure 115, shows a brass socket threaded for J^-inch 
pipe, and which is designed to be used with portable cord. 
Care should be taken in making up these sockets to see that 
the knot under the head of .the socket has a good bearing 
surface so that it will not pull through the larger bushing, 
these portables being very apt to be jerked about. 

A lamp guard to be of any value should be so constructed 
that the bulb of .the lamp cannot come in contact with any- 
thing outside of the lamp guard ; it should also protect the 
lamp from any sudden jar. The design of the guard should 
be such that it can be firmly attached to the socket so it will 
no.t work loose and come in contact with the live butt of the 
lamp or projecting threaded portion of the socket. 

e. Must not be used in show windows except when pro- 
vided with an approved metal armor. 

The great number of fires which have been caused by the 
use of flexible cord in show windows is sufficient argument 
against its use. 

/. Must be protected by insulating bushings where .the 
cord enters the socket. 

g. Must be so suspended that the entire weight of the 
socket and lamp will be borne by some approved device under 
the bushing in the socket, and above the point where .the cord 
comes through the ceiling block or rosette, in order that the 
strain may be taken from the joints and binding screws. 

This Is usually accomplished by knots In the cord inside 
the socket and rosette. 

Special ceiling blocks or rosettes which facilitate the 
fastening of cords are on the market and should be used. In 
fastening the cord to sockets the end of the cord should be 
soldered. This does away with the liability of stray strands 



LOW POTENTIAL SYSTEMS. 



197 



short circuiting on the shell of the socket and also affords a 
better and stronger contact under the binding screws. This 
soldering is best done by dipping the ends of the cord in melted 
solder. If a blow torch is used the small wires are very easily 
overheated and the soldering may do more harm than good. 
It is also well to tape .the ends of cords, leaving only just 
enough bare metal to go under the binding screws ; the tape 
will hold the end of the braid and will confine any ends of 
wires which do not happen to come under the binding screws. 

29. Arc Lamps on Constant-Potential Circuits. 

a. Must have a cut-out (see No. .17 a) for each lamp or 

each series of lamps. 

The branch conductors should have a carrying" capacity 
about 50 per cent in excess of the normal current required by 
the lamp to provide for heavy current required when lamp !■ 
started or when carbons become stuck without overfusing the 
wires. 

Figure 116 at the left gives a diagram of a constant poten- 
tial arc circuit as generally used at present for enclosed arc 




Figure 116. 



lamps. Each arc lamp of this kind requires a pressure of 110 
volts. A steadying resistance, R, is always placed in series 
with constant potential lamps, its object being to keep down 
the current while the lamp feeds. During the short time that 



198 MODERN ELECTRICAL CONSTRUCTION. 

the two carbons are together, the resistance of the lamp is so 
low that an enormous amount of current would flow were it 
not for this resistance. With mos.t lamps this resistance is 
now installed in the hood. Since the rule requires a carrying 
capacity about 50 per cent in excess of the normal current for 
branch conductors, it would be well to provide this also for 
mains in such cases where groups of arc lamps are likely to 
be controlled by one switch and used .together. 

Figure 116 at the right shows a diagram of wiring for 
open arc lamps. Two lamps are usually run in series on 110 
volts together with a steadying pressure. An open arc does 
not work well with a pressure higher than about 45 volts. 

b. Must only be furnished with such resistance or regula- 
tors as ?re enclosed in non-combus.tible material, such resist- 
ances being treated as sources of heat. Incandescent lamps 
must not be used for this purpose. 

c. Must be supplied with globes and protected by spark 

arresters and wire netting around the globe, as in the case of 

series arc lamps (see Nos. 19 and 58). 

Outside arc lamps must be suspended at least eig-ht feet 
above sidewalks. Inside arc lamps must be placed out of reach 
or suitably protected. 

d. Lamps when arranged to be raised and lowered, either 
for carboning or other purposes, shall be connected up with 
stranded conductors from the last point of support to the 
lamp, when such conductor is larger tha'n No. 14 B. & S. 
gage. 

30. Economy Coils. 

a. Economy and compensator coils for arc lamps must be 
mounted on non-combustible, non-absorptive insulating sup- 
ports, such as glass or "porcelain, allowing an air space of at 
least one inch between frame and support, and muct in gen- 
eral be treated as sources of heat. 

31. Decorative Lighting Systems. 

a. Special permission may be given in writing by the 



LOW rOTENTIAL SYSTEMS. 199 

Inspection Department having jurisdiction for the temporary 
installation of approved Systems of Decorative Lighting, pro- 
vided the difference of potential between the wires of any 
circuit shall not be over 150 volts and also provided that no 
group of lamps requiring more than 1,320 watts shall be de- 
pendent on one cut-out. 

No "System of Decorative Lighting" to be allowed under 
this rule which is not listed in the Supplement to the National 
Electrical Code containing list of approved fittings. 

31 A. Theater Wiring. 

(For rules governing Moving Picture Machines see No. 

65 A.) 

All wiring apparatus, etc., not specifically covered by 
special rules herein given must conform to the Standard Rules 
and Requirements of the National Electrical Code. 

In so far as these Rules and Requirements are concerned, 
the term ''theater^' shall mean a building or part of a build- 
ing in which it is designed to make a presentation of dramatic, 
operatic or other performances or shows for the entertain- 
ment of spectators which is capable of seating at least four 
hundred persons, and which has a stage for such perform- 
ances that can be used for scenery and other stage appliances. 

A. Services. 

1. Where source of supply is outside of building there 
must be at least two separate and distinct services where 
practicable, fed from separate street mains, one service to be 
of sufficient capacity to supply current for the entire equip- 
ment of theater, while the other service mus.t be at least of 
sufficient capacity to supply current for all emergency lights. 

By "emergency lights" are meant exit lights and all lights 
in lobbies, stairways, corridors and other portions of theater 
to which the public have access which are normally kept 
lig-hted during: the performance. 

2. Where source of supply is an isolated plant within 
same building, an auxiliary service of at least sufficient ca- 
pacity to supply all emergency lights must be installed from 
some outside source, or a suitable storage battery within 



200 



MODERN ELECTRICAL CONSTRUCTION. 



the premises may be considered the equivalent of such serv- 
ice. 

The spirit of this rule requires that the ^'emergency" light- 




Erme:ge:nc> 

LiGMT 

Circuits 



Ma)n ForHo*jse and Stage. 



ETMeRGEMCv 
Service. 



Main 
Servicc. 



Figure 117. 

ing system be kept entirely separate and distinct from the 
general lighting system. The emergency lighting system is 



LOW POTENTIAL SYSTEMS. 



201 



designed to provide illumination sufficient for the audience to 
get from the auditorium to the outside of the building under 
any and all conditions liable to exist, even where the general 
illuminating system has been rendered useless. It is, there- 
fore, of the utmost importance that the emergency system be 
made as reliable as is possible to the end that under no con- 
dition liable to exist will these lights be out of service. Fig- 
ure 117 shows how this rule and also e-4 may be complied 
with. The emergency circuit should if possible be taken 
from -mains that have no connection whatever with those 
supplying the auditorium and stage lights. The emergency 
mains must lead to the lobby and are not allowed to have 
any fuses except those at the street and those finally pro- 
tecting the branch circuits. Under certain interpretation of 
this rule it is permissible to connect the two systems as 




Figure 118. 



shown by dotted lines. This is, however, bad practice, as 
the switch may be unintentionally left as shown in the cut 
and thus when the main fuse blows all of the lights will be 



202 



MODEKN ELECTRICAL CONSTRUCTION. 



out. In many cases this arrangement will be very costly," 
as often lobby and theater mains do not run close together. 
As there is to be only one fuse between street and cut-out 
box, the mains to lobby will have to be of the same size as 
the house mains. 

It will be a good plan to arrange the house mains as 
shown in Figure 118. The double throw switch is provided 





Figure 119. 

merely to enable a quick re-illumination to take place in case 
one of the fuses were to blow. The switch is located at the 



LOW rOTENTIAL SYSTEMS. 



203 



electrician's station and it is but necessary for him to throw 
the switch to the other side to light up the house again. 

In order to be certain that the fuse in the street will not 
blow, .the wires between street and switch may be made sev- 
eral sizes heavier than required and fuse accordingly. Under 
such circumstances it is extremely unlikely that any but the 
fuse at the electrician's station will blow. 

b. Stage. 

1. All permanent construction on stage side of pro- 
scenium wall must be approved conduit, with the exception 
of border and switchboard wiring. 

2 Switchboards. — Must be made of non-combustible, 
non-absorptive material, and where accessible from stage 
level must be protected by an approved guard-rail to prevent 
accidental contact with live parts on the board. 

The switchboard of necessity being close to the stage 
proper is generally in such a position that persons leaving 
the stage pass directly in front of it. As the costumes worn 
by actors are very often made up of tinsel or other conduct- 




Figure 120. 



ing material, and as various metal trappings are carried, it 
is essential that the guard rail be of such design as to pre- 



204 MODERN ELECTEICAL CONSTRUCTION. 

vent these materials from coming in contact with the live 
parts of the board. Where the guard rail is placed close to 
the board it is often advisable to provide a screen between 
the guard rail and the floor. 

3. Footlights. 

a. Must be wired in approved conduit, each lamp recep- 
tacle being enclosed within an approved outlet box, the whole 
to be enclosed in a steel trough, metal to be of a thickness 
not less than No. 20 gage, or each lamp receptacle may be 
mounted on or in an iron or steel box so constructed as to 
enclose all the wires and live parts of receptacles. 

b. Must be so wired that no set of lamps requiring more 
than 1,320 watts will be dependent on one cut-out. 

Figure 119 shows a number of forms in which footlight 
troughs are made up. These troughs are constructed of 
No. 20 Stubbs gage iron or steel, the receptacles being 
attached to the upper section as shown in Figure 120. The 
completed footlight strip is shown in Figure 121. These 




Figure 121. 

strips are combined in various ways to make up the foot- 
light proper, their arrangement depending on the lighting 
effect desired. A common arrangement is shown in Figure 
122, where two separate strips are used, one elevated above 
the other in order that the light from the back row of lamps 
will not be obstructed by the lamps in the front row. When 
footlights are installed in this manner more light is ob- 
tained when the clear lamps are placed in the front row, as 
only a small part of the light emitted from the colored lamps 



LOW POTENTIAL SYSTEMS. 



205 



will be absorbed by passing through the clear globes, while, 
with the reverse arrangement, where the colored lamps are 
placed in the front row, a considerable amount of light would 
be absorbed by the light from the clear lamps passing 
through the colored glass. Owing to the fact that the foot- 
lights are generally placed in troughs cut in the stage floor, 
thus bringing the lamps below the level of the stage floor, 
the placing of the white lamps in the lower row would not 




Figure 122. 

allow sufficient light to illuminate the back part of the stage, 
and for this reason where footlights are placed as shown 
in the figure it is the usual practice to place the white lights 
in the upper row. 

Where all the lamps, both white and colored, are placed 



xO^a-a^a-o^o-Q- 



Figure 123. 



in one row, a reflector of the design shown in Figure 123 
will ruiaterially increase the useful light. 

Recep.tacles used in footlight construction must be of ap- 
proved design and where the receptacle is fastened to the 



206 MODERN ELECTRICAL CONSTRUCTION. 

metal work with porcelain or metal threaded rings the re- 
ceptacle must be so designed that it cannot be turned by the 
insertion or extraction of the lamp. This is generally 
accomplished by means of notches or projections on the 
porcelain of the receptacle and the metal should always be 
stamped to fit these parts. 

Double braid, rubber covered wire must be used, and, 
with clip sockets, the wire must be soldered to the clip, in 
addition to being fastened by the binding screws. If the 
porcelain of the receptacle does not provide proper protec- 
tion all exposed contacts, including the clips themselves, 
should be taped or covered with a suitable compound. Com- 
pound should not be used on border lights, as the heat from 
the lamps will cause the compound to melt and run down on 
the lamps. This also applies to any device of this form 
where the lamp hangs down, or below, the trough. In cases 
of this kind the clips should be taped, or, better, properly 
designed receptacles used. 

The footlight circuits may be wired for a capacity of 1,320 
watts, this allowing 24-16 c. p. lamps, 18-24 c. p. lamps, or 
12-32 c. p. lamps on one circuit. 

4. Borders. 

a. Must be constructed of steel of a thickness not less 
than No. 20 gage, treated to prevent oxidation, be suitably 
stayed and supported by a metal framework, and so designed 
that fianges of reflectors will protect lamps. 

b. Must be so wired that no set of lamps requiring more 
than 1,320 watts will be dependent upon one cut-out. 

c. Must be wired in approved conduit, each lamp recep- 
tacle to be enclosed within an approved outlet box, the whole 
to be enclosed in a steel trough, or each lamp receptacle may 
be mounted on or in the cover of a steel box so constructed 
as to enclose all the wires and the live parts of receptacles, 
metal to be of a thickness not less than No. 20' gage. 

d. Must be provided with suitable guards to prevent 



LOW POTENTIAL SYSTEMS. 



207 



scenery or other combustible material coming in contact with 
lamps. 

e. Cables must be continuous from stage switchboard to 
border; conduit construction must be used from switchboard 
to point v/here cables must be flexible to permit of the rais- 
ing and lowering of border, and flexible portion must be 
enclosed in an approved fireproof hose or braid and be suit- 
ably supported. 

Junction Boxes will be allowed on fly floor and rigging loft 
In existing theaters where the wiring has been completed and 
approved by Inspection Department having jurisdiction. 

/. For the wiring of the border proper, wire with slow 
burning insulation should be used. 

g. Must be suspended with wire rope, same to be in- 
sulated from border by at least two approved strain insulators 
properly inserted. 

The design and construction of border lights is similar 
to that just described for footlights with the exception of 
the arrangement of the strips and the kind of wire used. 
Border lights are suspended above the stage and are de- 
signed to throw the light downward and slightly to the back 
of the stage. To produce the proper lighting effects the 



V. 




J 



.H 



? 



Figure 124. 

border must be capable of adjustment, both as to its height 
above the stage and its position. 

Figure 124 shows several forms of border lights. 



208 MODERN ELECTRICAL CONSTRUCTION. 



Figure 125 shows a simple form of border light in com- 
mon use. It will be noticed that the flange of the reflector is 
carried around the lamps in such a manner as to protect 
them from accidental contact with the scenery. 



Figure 125. 

Figure 126 shows a completed border light with one 
method of suspension. The iron bands to which are fas- 
tened the supporting chains are carried entirely around the 
border frame and serve as a means of attaching it to its 
support and at the same time provide mechanical protec- 
tion for the lamps. These bands are placed from four to 
six feet apart. 




Figure 126. 

The cables which carry current to the border lights are 
generally made up for each individual installation, the size 
and number of wires varying according to the number and 



LOW POTENTIAL SYSTEMS. 209 

corrtbinatian of lamps used and the distance of the border 
from the stage switchboard or center of distribution* 

There are at the present time no specifications govern- 
ing the construction of border light cable, but in a general 
way it should comply with the following : The wire of the 
cable should be stranded, the wires composing the strands 
to be of such size as will allow of sufficient flexibility with 
the required strength. Each of the stranded wires should 
be covered with a wind of cotton as required for flexible 
cord and should then be covered with a rubber covering of 
about the same thickness as required for rubber covered 
wires of corresponding sizes. Each wire should -have a stout 
braid which should be filled with a waterproofing compound. 
To round out the cable, jute, slightly impregnated with a 
waterproof compound, should be used. The whole cable 
should be covered with a tough outer braid of such thick- 
ness as to provide proper protection with continued rough 
usage. No rubber need be used between this outer braid and 
the individual wires comprising the cable. 

In reference to the above specifications it might be well 
to state .that they are given simply as a guide to enable one 
to choose a cable suitable to the work. There are at the 
present .time no Underwriters' specifications covering this 
class of wire and there is considerable cable in use which 
is entirely unsuited to the purpose. The latest Underwriters' 
rules should be consulted before buying or ordering cable. 

Border cables must be continuous from the stage switch- 
board or center of distribution to the border itself, the ex- 
posed portion of the cable being protected by a fireproof 
braid or hose. This fireproof covering can be put on when 
the cable is manufactured or fireproof hose suitable for 
the purpose may be obtained from the manufacturers of this 
class of goods and placed on the ordinary cable. The cables 



210 MODERN ELECTRICAL CONSTRUCTION. 

should be long enough to allow .the border to be lowered to 
within six or seven feet of the floor to permit of the neces- 
sary repairs and adjustments and the replacement of lamps. 

"Take-up" devices, which are attached to the cable to take 
up the slack when the border is raised, should be fastened 
to the cable by some suitable device which will give a large 
bearing surface so that the insulation of the cable will not 
be injured. The practice of simply tying a rope around the 
cable -is very bad, as the rope is sure to cut into the insula- 
tion. 

As considerable heat is developed in a border light, due 
to the great number of lamps employed and to the position 
of the border itself, the rubber covering of the ordinary 
rubber covered wire would be very apt to become useless 
as an insulator, so that for this class of wiring slow-burning 
wire should be used. Specifications covering this wire are 
given under ''Fittings." 

Wire rope must be used for the suspension of the border 
lights. The rope should be of such size as to properly sup- 
port the border with an ample safety factor. Generally 
three or four ropes are provided, each rope being fastened 
to a bridle which will distribute the s.train uniformly along 
the length of the border frame. Two strain insulators of 
the type shown in Figure 49 should be connected in the 
cable at the point where it connects to .the border. The sup- 
porting cables are generally run to counterweights, hemp 
ropes fastened to either the counterweights or the border 
itself serving as a means to raise and lower the border. 
Where the border is small and of inconsiderable weight the 
wire rope is run directly to the point of fastening and the 
adjustments made with it direct. 

5. Stage Pockets. — Must be of approved type controlled 
from switchboard, each receptacle to be of not less than fifty 



LOW POTENTIAL SYSTEMS. 



211 



amperes rating, and each receptacle to be wired with a 
separate circuit to its full capacity. 

For the connection of portable apparatus on the stage, 





Figure 127. 

pockets are provided in the stage floor. These pockets con- 
tain receptacles into which the plugs connected to cables 
attached to the apparatus are inserted. The pockets should 
be made absolutely fireproof and .the receptacles should be 
so installed that all live parts will be clear of the opening. 
It would be a good rule to have stage plugs of different 
shapes to be used in connection with arc and incandescent 
lights, so that it will be impossible to plug incandescent 
lights on arc light circuits. An arc light circuit requires a 
fuse of about forty amperes. Many times a single incan- 
descent light is plugged into such a circuit. A short circuit 
occurring under .these circumstances would be accompanied 
with disastrous results. Figure 127 shows a s.tage pocket 



212 MODERN ELECTRICAL CONSTRUCTION. 

with receptacles. The average stage pocket accommodates 
four receptacles. 

6. Proscenium Side Lights. — Must be so installed that 
they canno.t interfere with the operation of or come in con- 
tact with curtain. 

Those lights placed at the stage opening on the stage 
side of the wall which separates the stage from the audi- 
torium (proscenium wall) are known as the proscenium 
side lights. They are constructed in the same manner as 
the footlights previously described, with the exception of 




Figure 12 



the reflectors, which are of various shapes. Figure 128 
shows a common form of proscenium side light. 

The troughs are generally hinged so that they may be 
turned to illuminate any particular part of the stage, and 
special care should be exercised in placing them so that 
they cannot in any manner interfere with the operating of 
the curtain. It is sometimes advisable, especially in the case 
of vaudeville or burlesque houses, to provide a wire mesh 
screen for the protection of the lamps. 

7. Scene Docks. — Where lamps are installed in Scene 
Docks, .they must be so located and installed that they will 
not be liable to mechanical injury. 



LOW POTENTIAL SYSTEMS. 213 

As scene docks are often used for the storage of scenery 
and other stage paraphernalia and as Hghts are generally 
placed on the side walls, a substantial guard should be pro- 
vided. This guard should be capable of standing considerable 
hard usage and should be hrmly attached. The ordinary 
lamp guard fastened to the socket or lamp itself is useless as 
a protection. 

8. Curtain Motors. — Must be of ironclad .type and in- 
stalled so as to conform to the requirements of the National 
Electrical Code. (See No. 8.) 

Rheostats used with curtain motors, if installed on the 
stage wall or in any o.ther location outside of the motor 
room, should be entirely enclosed and well protected, so that 
nothing of an inflammable nature can come in contact with 
them. 

9. Control for Stage Flues/ 

a. In cases where dampers are released by an electric 
device, the electric circuit operating same must be normally 
closed. 

b. Magnet operating damper must be wound to take full 
voltage of circuit by which it is supplied, using no resist- 
ance device, and must not heat more than normal for ap- 
paratus of similar construction. It must be located in loft 
above scenery and be installed in a suitable iron box with a 
tight self-closing door. 

c. Such dampers must be controlled by at least two 
standard single pole switches mounted within approved iron 
boxes provided with self-closing doors without lock or 
latch, and located, one at the electrician's station, and others 
as designated by .the Inspection Department having jurisdic- 
tion. 

The dampers referred to are ventilators arranged above 
the stage and scenery. In case of fire it is essential that 
these be opened immediately to allow smoke to escape and 



214 



MODEIIN ELECTKICAL CONSTKUCTION. 



also to prevent the to.tal consumption of oxygen in the build- 
ing by the flames. This rapid consumption of oxygen, mak- 
ing it very difficult for people to breathe, thereby causing 
frantic efforts at inhalation, which result in inhaling large 
quantities of smoke and overheated air, are perhaps .the 
main causes of the enormous death loss usual in theater 
fires. 

Where current is obtained from an isolated plant which 
is shut down at night time and is not supplied with storage 

-p — 1 




Figure 129. 



battery, or where alternating current is used, it is generally 
more satisfactory to use battery current for the operation 
of the damper, gravity cells being used for this purpose. 
Where the installation is supplied by a direct current system 
which is continuous .tha damper circuit may be taken directly 
from the system. Figure 129 shows an inexpensive form of 
damper control which is supplied by current from two or 
three cells of gravity battery. The lever arms are made 
from bar iron formed in the shapes shown. The magnet 



LOW POTENTIAL SYSTEMS. 215 

is of the type used in door openers and is enclosed in an 
iron box, that part of the enclosure immediately surround- 
ing .the magnet pole pieces being of brass. When the cir- 
cuit is opened the armature falls and strikes the lower arm 
a sharp blow, thus releasing the damper rope. To close 
the damper the circuit is first closed, the magnet armature 
is pulled back in place by the cord attached to the lower end 
of i.t, and the damper is closed, the ball in the damper rope 
engaging in the slot in the end of the lever arm. 

c. Dressing Rooms. 

1. Must be wired in approved conduit, except that in 
existing buildings where it is impracticable to install ap- 
proved conduit, approved armored cable may be used, pro- 
vided it is installed in accordance with No. 24 A. 

2. All pendant lights must be equipped with approved 
reinforced cord or cable. 

3. All lamps mtist be provided wath approved guards. 

Experience has proven it a difficult matter to arrange 
dressing rooms in such a way that actors cannot disar- 
range them and thus cause troubles of many kinds. One of 
the principal preventive devices is a lamp guard fastened to 
each socket in such a way that it cannot be removed with- 
out assistance from the house electrician. This will prevent 
the removal of the lamp and the substitution of a lamp of 
greater candle power or of the portable devices which many 
actors carry that require much more current. A lamp guard 
so arranged that it can be locked on will readily accomplish 
the purpose and such lamp guards are on the market. 

The principal use of light in the dressing rooms is for 
the "make-up" of the actors. One light on each side of 
every mirror, suitably placed, with one or two lights for gen- 
eral illumination, are generally sufficient. A receptacle for 



216 MODEEN ELECTRICAL CONSTRUCTION. 

curling iron connection can also be provided, but should also 
be under lock and key. 

d. Portable Equipments, 

1. Arc lamps used for stage effects must conform to .the 
following requirements : — 

a. Must be constructed entirely of metal except where 
the use of approved insulating material is necessary 

b. Must be substantially constructed, and so designed as 
to provide for proper ventilation, and to prevent sparks 
being emitted from lamps when same is in operation, and 
mica must be used for frame insulation. 

c. Front opening must be provided with a self-closing 
hinged door frame in which wire gauze or glass must be in- 
serted, excepting lens lamps, where the front may be sta- 
tionary and a soHd door be provided on back or side. 

d. Must be provided with a one-sixteen.th-inch iron or 
steel guard having a mesh not larger than one inch, and be 
substantially placed over top and upper half of sides and 
back of lamp frame ; this guard to be substantially riveted 
to frame of lamp, and to be placed at a distance of at least 
two inches from the lamp frame. 

e. Switch on standard must be so constructed that acci- 
dental contact with any live portion of same will be im- 
possible. 

/. All stranded connections in lamp and at switch and 
rheostat must be provided with approved lugs. 

g. Rheostat, if mounted on standard, must be raised to 
a height of at least .three inches above floor line, and in ad- 
dition to being properly enclosed must be surrounded with 
a substantially attached metal guard having a mesh not 
larger than one square inch, which guard is to be kept at 
least one inch from outside frame of rheostat. 

li. A competent operator must be in charge of each arc 
lamp, except that one operator may have charge of two 
lamps when they are not more than ten feet apart and are 
so located tha.t he can properly watch and care for both 
hmps. 

On the stage hand-feed arc lamps are used almost ex- 



LOW POTENTIAL SYSTEMS. 



217 



clusively and an operator is always required to look after 
the lamps. The style of lamps generally used are shown 
in Figures 130 and 131. Figure 130 shows the focusing or 




Figure 130. 




Figure 131, 



spot lamp and Figure 131 the open box or olivet lamp, which 
is used for general illumination. These arc lamps require a 



2U8 



MODERN ELECTRICAL CONSTRUCTION. 









j 


SSP- 




-XSQp. 




<: 




^ 


/ 













Rheostat No. 83. 

Hardline — One lamp on 220 
volts, 20 amperes. 
Dotted linei — One lamp on 
110 volts, 30 amperes. 



Rheostat No. 82. 

One lamp on 110 volts, 
60 amperes. 




Rheostat No. 83. 

Two lamps on 110 volts 
each, 15 amperes. 



Rheostat No. 82. 

Hard line— Two lamps on 220 volts 
each, 20 amperes. 
Dotted line — Two lamps on 110 
volts each, 30 amperes. 




Rheostat No. 82. 

One lamp on 22 J volts, 
35 amperes. 



-QSP 









Rheostat No. 82. 

One lamp on 450 volts, 
20 amperes. 



y 














Rheostat No. 81. 

One lamp on 550 volts, 22 amperes. 

Figure 132. 



LOW POTENTIAL SYSTEMS. 219 

current of from 20 to 40 amperes and should be wired for 
accordingly. 

Figure 132 shows diagrammatically a very useful form of 
rheostat for stage purposes. As most "shows'' are constantly 
traveling, the apparatus carried by them should be adjustable 
in so far as voltage is concerned and also as to system, i. e., 
alternating or direct current. As will be seen from the figure, 
this rheostat lends itself to any voltage or system. This 
particular rheostat is manufactured by the Chicago Stage 
Lighting Co. 

2. Bunches, a. Must be substantially constructed of 
metal and must not contain any exposed wiring. 

b. The cable feeding same must be bushed in an ap- 
proved manner where passing through the metal and must 
be properly secured to prevent any mechanical strain from 
coming on the connection. 

The bunch light is used in various locations around the 
stage where only a small amount of illumination is required. 

3. Strips, a. Must be constructed of steel of a thick- 
ness not less than No. 20 gage, treated to prevent oxidation, 
and suitably stayed and supported by metal framework. 

b. Cable feeding must be bushed in an approved manner 
where passing through the metal, and must be properly se- 
cured to prevent any mechanical strain coming on the con- 
nections. 

Strip lights are laid on the floor and hung on the scenery 
and are used to illuminate those parts of the scenery where 
the lights from the foots and borders is obstructed. Any 
of the forms shown in Figure 119 may be used for footlight 
construction. Reflectors are generally provided which serve 
to concentrate the light on the spot desired and to protect 
the lamps from accidental contact. Special care must be 
given to cables, where they leave strips; being portable, they 
soon suffer damage at these points. 



220 



MODERN ELECTRICAL CONSTRUCTION. 



4. Portable Plugging Boxes. — Must be constructed so 
that no current carrying part will be exposed, and each re- 
ceptacle must be protected by approved fuses mounted on 
slate or marble bases and enclosed in a fireproof cabinet 
equipped with self-closing doors. Each receptacle must be 
constructed to carry thirty amperes without undue heating, 
and the bus-bars must have a carrying capacity equivalent to 




Figure 133. 



the current required for the .total number of receptacles, 
allowing thirty ampere* to each receptacle, and approved lugs 
must be provided for the connection of the master cable. 

When a number of pieces of electrical apparatus are to be 
used at one time on the stage, instead of carrying a separate 
cable from each piece of apparatus to a pocket, a portable 



LOW rOTEXTlAL SYSTEMS. 



221 



plugging box or spider box is used. This is shown in Figure 
133. One large cable is carried from the plugging box to a 
pocket or other convenient point of connection and the 
various pieces of apparatus connected to .the plugging box 
by plugs and short cables. This greatly reduces the amount 
of cable used and allows of rapid assembly and removal. 

5. Pin Plug Conductors, a. When of approved type 
may be used to connect approved portable lights and ap- 
pliances. 

h. Must be so installed that the ''female*' part of plug 
will be on the live end of cable and must be so constructed 




Figure 134. 

that tension on the cable will not cause any serious mechan- 
ical strain on the connections. 

6. Lights on Scenery. — When brackets are used they must 
be wired entirely on the inside, fixture stem must come 
through to the back of the scenery and end of s.tem be 
properly bushed. 

The usual method of complying with this rule is shown in 



222 



MODERN ELECTRICAL CONSTRUCTION. 



Figure 134. Everything a1)0ut the bracket is of metal and 
stage cable is used to make the connection to the outside. 

7. String or Festoon Lights. — Wiring for same should be 
approved cable, joints where taps are taken from same for 
lights to be properly made, soldered and taped, and where 
lamps are used in lanterns or similar devices lamps must be 
provided with approved guards. Where taps are taken from 
cable, they should be so staggered that joints of different 
polarity will not come immediately opposite each other and 
must be properly protected from strain. 




iti i£li.^^>^jj^jj^^^^ 



Figure 135. 



A good method of making tap joints in festoons is 
shown in Figure 135. The joints are made staggering and 
properly soldered and taped with both rubber and friction 
tape. The cable which is tapped on is then carried along 
the main cable for three or four inches and securely taped. 
This removes nearly all the strain from the joints and pre- 
vents the wires from working loose. 

8. Special Electrical Effects. — Where devices are used 
for producing special effects, such as lightning, waterfalls, 
etc., the apparatus must be so constructed and located that 
flames, sparks, etc., resulting from the operation cannot come 
in contact with combustible ma.terial. 

The necessity for electrical current in connection with 
stage effects has of late years been greatly reduced. Scenes 
and effects of almost any description can be produced by 



LOW POTENTIAL SYSTEMS. 



223 



means of transparent films attached to and rotating in front 
of an arc lamp. Celluloid films, if they remain stationary 
exposed to the light of an arc lamp, may be ignited in two 
or three seconds and burn very rapidly. 

Care must be exercised in the use of some of these effects, 
as the sudden and unexpected production of a fire effect or 
of a puff of smoke or momentary blaze such as would be 
produced by a short circuit might have a disastrous effect 
on the audience. 

In Figure 136 a device is shown for producing lightning 
flashes. It consists of a solenoid, the core of which is at- 




Figure 136. 



tached to a lever fitted with a piece of carbon. The carbon 
rests on a piece of steel bar. When the circuit is closed 
the solenoid operates and raises the carbon from the piece 
of steel, a considerable flash resulting. The carbon continues 



224 MODERN ELECTRICAL CONSTRUCTION. 

to rise until the circuit opens, when it drops again, causing 
another flash, etc. 

e. Auditorium. 

1. All wiring must be installed in approved conduit, ex- 
cept that in existing buildings where it is impracticable to in- 
stall approzed conduit, approved armored cable may be used, 
provided it is installed in accordance with No. 24 A. 

2. All fuses used in connection with lights illuminating all 
parts of the house used by the audience must be installed 
in fireproof enclosures so constructed that there will be a 
space of at least six inches between the fuses and the sides 
and face of enclosure. 

3. Exit lights must not have more than one set of fuses 
between same and service fuses. 

The only fuses allowed on the exit light circuits are the 
branch fuses and the fuses at the service. This necessitates 
running the exit light main direct to the service, no.t changing 
size and not tapping onto any other main unless both mains 
are of equal carrying capacity. 

4. Exit lights and all lights in halls, corridors or any 
other part of the building used by .the audience, except the 
general auditorium lighting, must be fed independently of the 
stage lighting, and must be controlled only from the lobby 
or other convenient place in front of the house. 

All sockets used on the exit and emergency lighting should 
be of the keyless type, so that they cannot be controlled from 
any point except the lobby. 

5. Every portion of the theater devoted to the use or ac- 
commodation of the public, also all outlets leading to the 
streets and including *all open courts, corridors, stairways, 
exits and emergency exit stairways, should be well and prop- 
erly lighted during every performance, and the same should 
remain lighted until the entire audience has left the premises. 

To conform with this rule there should be provided in 



LOW rOTENTIAL SYSTEMS. 225 

the auditorium a sufficient number of lights to properly il- 
luminate it at all times. These lights should never be turned 
out while the audience is in the building. They should be 
supplied with current from the emergency mains and should 
be controlled from the lobby. 

32. Car Wiring and Equipment of Cars. 

a. Protection of Car Body, etc, 

1. Under side of car bodies to be protected by approved 
fire-resisting, insulating material, not leess than 1-8 inch in 
thickness, or by sheet iron or steel, not less than .04 inch 
in thickness, as specified in Section a, 2, 3 and 4. This pro- 
tection to be provided over all electrical apparatus, such as 
motors with a capacity of over 75 H. P. each, resistances, con- 
tactors, lightning arresters, air-brake motors, etc., and also 
where wires are run, except that protection may be omitted 
over wires designed to carry 25 amperes or less if they are 
encased in metal conduit. 

2. At motors of over 75 H. P. each, fire-resisting mate- 
rial or sheet iron or steel .to extend not less than 8 inches 
beyond all edges of openings in motors and not less than 6 
inches ibeyond motor leads on all sides. 

3. Over resistances, contractors and lightning arresters, 
and other electrical apparatus, excepting when amply pro- 
tected by their casing, fire-resis.ting material or sheet iron or 
steel to extend not less than 8 inches beyond all edges of the 
devices. 

4. Over conductors, not encased in conduit, and con- 
ductors in conduit when designed to carry over 25 amperes, 
unless the conduit is so supported as to give not less than 
54 inch clear air space between the conduit and the car, fire- 
resisting material or sheet iron or steel to extend at least 6 
inches beyond conductors on either side. 

The fire-resisting- insulating material or sheet iron or 
steel may be omitted over cables made up of flame-proof 
braided outer covering- when surrounded by 1-8 inch flame- 
proof covering, as called for by Section i, 4. 

5. In all cases fireproof material or sheet iron or steel 



226 MODERN ELECTRICAL CONSTRUCTION. 

to have joints well fitted, to be securely fastened to the sills, 
floor timbers and cross braces, and to have the whole sur- 
face treated with a waterproof paint. 

6. Cut-ou.t and switch cabinets to be substantially made 
of hard wood. The entire inside of cabinet to be lined with 
not less than 1-8 inch fire-resisting insulating material which 
shall be securely fastened to the woodwork, and after the 
fire-resisting material is in place the inside of .the cabinet 
shall be treated with a waterproof paint. 

b. Wires, Cables, etc. 

1. All conductors to be stranded, the allowable carrying 
capacity being determined by Table "A" of No. 16, except that 
motor, .trolley and resistance leads shall not be less than No. 
7 B. & S. gage, heater circuits not less than No. 12 B. & S. 
gage, and lighting and other auxiliarv circuits not less than 
No. 14 B. & S. gage. 

The current used in determining the size of motor, trolley 
and resistance leads shall be the per cent of .the full load 
current, based on one hour's run of the motor, as given by 
the following table : 

Size each Motor Trolley Resistance 

motor. Leads. Leads. Leads. 

75 H. P. or less 50% 40% 15% 

Over 75 H. P. 45% 35% 15% 

Fixture wire complying with No. 46 will be permitted for 

wiring approved clusters. 

2. To have an insulation and braid as called for by No. 
41 for wires carrying currents of the same potential. 

3. When run in metal conduit, to be protected by an 
additional braid as called for by No. 47. 

Where conductors are laid in coaduiL, not being drawn 
through, the additional braid will not be required. 

4. When not in ^ conduit, in approved moulding, or in 
cables surrounded by % inch flameproof covering, must com- 
ply with the requirements of No. 41 (except that tape may be 
substituted for braid) and be protected by an additional 
flameproof braid, at least 1-32 inch in thickness, the outside 
being saturated with a preservative flameproof compound. 



LOW POTENTIAL SYSTEM^. 227 

This rule will be interpreted to include the leads from the 
motors. 

5. Must be so spliced or joined as to be both mechan- 
ically and electrically secure without solder. The joints must 
then be soldered and covered with an insulation equal to that 
on the conductors. 

Joints made with approved splicing devices and those con- 
necting- the leads at motors, plows or third rail shoes need 
not be soldered. 

6. All connections of cables to cut-outs, switches and 
fittings, except those to controller connection boards, when 
designed to carry over 25 amperes, must be provided with 
lugs that will grip .the conductor between the screw 
and the lug, the screws being provided with flat washers ; or 
by block terminals having two set screws, and the end of 
the conductors must be dipped in solder. Soldering, in ad- 
dition to the connection of the binding screws, is strongly 
recommended, and will be insisted upon when above require- 
ments are not complied with. 

This rule will not be construed to apply to circuits where 
the maximum potential is not over 25 volts and current does 
not exceed 5 amperes. 

c. Cut-outs, Circuit Breakers and Szvitches. 

1. All cut-outs and switches having exposed live metal 
parts to be located in cabinets. Cut-outs and switches, not 
in iron boxes or in cabinets, shall be mounted on not less 
than ^ inch fire-resis.ting insulating material, which shall pro- 
ject at least J/2 inch beyond all sides of the cut-out or switch. 

2. Cut-outs to be of the approved cartridge or approved 
blow-out type. 

3. All switches controlling circuits of over 5 ampere 
capacity shall be of approved single pole, quick break or ap- 
proved magnetic blow-out type. 

Switches controlling circuits of 5 ampere or less capacity 
may be of the approved single pole, double break, snap type. 

4. Circuit breakers to be of approved type. 

5. Circuits must not be fused above their safe carrying 
capacity. 

6. A cut-out must be placed as near as possible to the 



228 MODERN ELECTRICAL CONSTRUCTION. 

current collector, so that the opening of the fuse in this 
cut-out will cut off all current from the car. 

When cars are operated by metallic return circuits, with 
circuit breakers connected to both sides of the circuit, no 
fuses in addition to the circuit breakers will be required. 

d. Conduit. 

When from the nature of the case, or on account of the 
size of the conductors, the ordinary pipe and junction box 
construction is not permissible, a special form of conduit 
system may be used, provided the g"eneral requirements as 
given below are complied with. 

1. Metal conduits, outlet and junction boxes to be con- 
structed in accordance with Nos. 49 and 49A, except that 
conduit for lighting circuits need not be over 5-16 inch inter- 
nal diameter and 1-2 inch external diameter, and for heating 
and air motor circuits need not be over 3-8 inch internal 
diameter and 9-16 inch external diameter, and all conduits 
where exposed to dampness must be water tight. 

2. Must be continuous between and be firmly secured 
into all outlet or junction boxes and fittings, making a 
thorough mechanical and electrical connection between same. 

3. Metal conduits, where they enter all outlet or junction 
boxes and fittings, must be provided with approved bushings 
fitted so as to protect cables from abrasion. 

4. Except as noted in Section f, 2, must have the metal 
of the conduit permanently and effectively grounded. 

5. Junction and outlet boxes must be installed in such a 
manner as to be accessible. 

6. All conduits, outlets or junction boxes and fittings to 
be firmly and substantially fastened to the framework of the 
car. 

e. Moulding 

1. To consist of a backing and a capping and to be con- 
structed of fire-resisting insulating material, except that it 
may be made of hard wood where the circuits which it is 
designed to support are normally not exposed to moisture. 



LOW rOTEXTIAL SYSTEMS. 229 

2. When constructed of tire-resisting insulating material, 
the backing shall be not less than 1-4 inch in thickness and 
be of a width sufficient to extend not less than 1 inch beyond 
conductors at sides. 

The capping, to be not less than Vs inch in thickness, 
shall cover and extend at least M inch beyond conductors on 
either side. 

The joints in the moulding shall be mitered to fit close, the 
whole material being firmly secured in place by screws or 
nails and treated on the inside and outside with a waterproof 
paint. 

When fire-resisting moulding is used over surfaces already 
protected by 1-8 inch fire-resisting insulating material no 
backing will be required. 

3. Wooden mouldings must be so constructed as to thor- 
oughly encase the wire and provide a thickness of not less 
than 3-8 inch at the sides and back of the conductors, the 
capping being not less than 3-16 inch in thickness. Must have 
both outside and inside two coats of waterproof paint. 

The backing and the capping shall be secured in place by 
screws. 

f. Lighting and Lighting Circuits 

1. Each outlet to be provided with an approved porcelain 
receptacle, or an approved cluster. No lamp of over 32 
candle power .to be used. 

2. Circuits to be run in approved metal conduit or ap- 
proved moulding. 

3. When metal conduit is used, except for sign lights, 
all outlets to be provided with approved outlet boxes. 

4. At outlet boxes, except where approved clusters are 
used, porcelain receptacles to be fastened to the inside of 
the box and the metal cover to have an insulating bushing 
around opening for the lamp. 

When approved clusters are used, the cluster shall be 
thoroughly insulated from the metal conduit, being mounted 
on a block of hard wood or fire-resisting insulating mate- 
rial. 



230 MODERN ELECTRICAL CONSTRUCTION. 

5. Where conductors . are run in moulding the porce- 
lain receptacles or cluster to be mounted on blocks of hard 
wood or of fireproof insulating material. 

g. Heaters and Heating Circuits 

1. Heaters to be of approved type. 

2. Panel heaters to be so constructed and located that 
when heaters are in place all current carrying parts will be 
at leas.t 4 inches from all woodwork. 

Heaters for cross seats to be so located that current 
carrying parts will be at least 6 inches below under side of 
seat, unless under side of seat is protected by not less than 
1-4 inch fire-resisting insulating material, or .04 inch sheet 
metal with 1 inch air space over same, when the distance 
may be reduced to 3 inches. 

2. Circuits to be run in approved metal conduit, or in 
approved moulding, or if the location of conductors is such 
as will perfnit an air space of not less than 2 inches on all 
sides except from the surface wired over they may be sup- 
ported on porcelain knobs or cleats, provided the knobs or 
cleats are mounted on not less than 1-4 inch fire-resisting in- 
sulating material extending at leas.t 3 inches beyond con- 
ductors at either side, the supports raising the conductors 
not less than 1-2 inch from the surface wired over and being 
not over 12 inches apart. 

h. Air Ftimp Motor and Circuits. 

1. Circuits to be run in approved metal conduit or in 
approved moulding, except that when run below the floor 
of the car they may be supported on porcelain knobs or cleats, 
provided the supports raise the conductor at least 1-2 inch 
from the surface wired over and are not over 12 inches 
apart. 

2. Automatic control to be enclosed in approved metal 
box. Air pump and* motor, when enclosed, to be in ap- 
proved metal box or wooden box lined with metal of not 
less than 1-32 inch thickness. 

When conductors are run in metal conduits the boxes 
surrounding automatic control and air pump and motors may 
serve as outlet boxes. 



LOW POTENTIAL SYSTEMS. 231 



/. Main Motoy Circuits and Devices 

1. Conductors connecting between trolley stand and main 
cut-out or circuit breakers in hood to be protected where 
wires enter car to prevent ingress of mois.ture. 

2. Conductors connecting between third rail shoes on 
same truck to be supported in an approved ftre-resisting in- 
sulating moulding or in approved iron conduit supported by 
soft rubber or other approved insulating cleats. 

3. Conductors on .the under side of the car, except as 
noted in Section i, 4, to be supported in accordance with one 
of the following methods : 

a. To be run in approved metal conduit, junction boxes 
being provided where branches in conduit are made and 
outlet boxes where conductors leave conduit. 

b. To be run in approved fire-resisting insulating mould- 
ing. 

c. To be supported by insulating cleats, the supports 
being not over 12 inches apart. 

4. Conductors with flameproof braided outer covering, 
connecting between controllers a.t either end of car, or con- 
trollers and contactors, may be run as a cable, provided the 
cable where exposed to the weather is encased in a canvas 
hose or canvas tape, thoroughly taped or sewed at ends and 
where taps from the cable are made, and the hose or tape 
enters the controllers. 

Conductors with or without flameproof braided outer cov- 
ering connecting between controllers at either end of the 
car, or controllers and contactors, may be run as a cable, 
provided the cable throughout its entire length is surrounded 
by 1-8 inch flameproof covering, thoroughly taped or sewed 
at ends, or where taps from cable are made, and the flame- 
proof covering enters the controllers. , 

Cables where run below floor of car may be supported by 
approved insulating straps or cleats. Where run above floor 
of car, to be in a metal conduit or wooden box painted on the 
inside with not less than two coats of flameproof paint, and 
where this box is so placed that it is exposed to water, as by 
washing of the car floor, attention should be given to making 
the box reasonably waterproof. 



232 MODEKN ELECTRICAL CONSTRUCTION. 

. Canvas hose or tape, or flameproof material surrounding 
cables after conductors are in same, to have not less than 
two coats of waterproof insulating material. 

5. Motors to be so drilled that, on double truck cars, 
connecting cables can leave motor on side nearest to king 
bolt. 

6. Resistances to be so located that there will be at least 
6 inch air space between resistances proper and hre-resisting 
material of the car. To be mounted on iron supports, being 
insulated by non-combus.tible bushings or washers, or the 
iron supports shall have at least 2 inches of insulating sur- 
face between them and metal work of car, or the resistances 
may be mounted on hardwood bars, supported by iron stir- 
rups, which shall have not less than 2 inches of insulating 
surface between foot of resis.tance and metal stirrup, the 
entire surface of the bar being covered w^ith at least 1-8 inch 
fire-resisting insulating material. 

The insulation of the conductor, for about 6 inches from 
terminal of the resistance, should be replaced, if any in- 
sulation is necessary, by a porcelain bushing or asbestos 
sleeve. 

7. Controllers to be raised above platform of car by a 
not less than 1 inch hardwood block, the block being fitted 
and painted to prevent moisture working in between it and 
the platform. 

/. Lightning Arresters 

1. To be preferably located .to protect all auxiliary cir- 
cuits in addition to main motor circuits. 

2. The ground conductor shall be not less than No. 6 B. 
& S. gage, run with as few kinks and bends as possible, and 
be securely grounded. 

k. General Rules 

1. When passing* through floors, conductors or cables 
must be protected by approved insulating bushings, which 
shall fit the conductor or cable as closely as possible. 

2. Mouldings should never be concealed except where 
readily accessible. Conductors should never be tacked into 
moulding. 



LOW I'OTEXTIAL SYSTEMS. 233 

3. Short bends in conductors should be avoided where 
possible. 

4. Sharp edges in conduit or in moulding must be 
smoothed to prevent injury to conductors. 

33. Car Houses. 

• a. The trolley wires must be securely supported on in- 
sulating hangers. 

b. The trolley hangers must be placed at such a distance 
apart that, in case of a break in the trolley wire, contact 
with the floor cannot be made. 

c. Must have an emergency cut-out switch located at a 
proper place outside of the building, so that all the trolley 
wires in the building may be cut out at one point, and line 
insulators must be installed, so that when this emergency 
switch is open, the trolley wire will be dead at all points 
within 100 feet of the building. The current must be cut 
out of the building when not needed for use in the build- 
ing. 

This maj^ be done by the emergency switch, or if preferred 
a second switch may be used that will cut out all current from 
the building-, but w^liich need not cut out the trolley wire 
outside as would be the case w^ith the emerg-ency switch. 

d. All lamps and stationary motors must be installed 
in such a w^ay that one main switch may control the whole 
of each installation, lighting and power, independently of the 
main cut-out switch called for in Section c. 

e. Where current for lighting and stationary motors is 
from a grounded trolley circuit, the following special rules 
to apply: 

1. Cut-outs must be placed between the non-grounded 
side and lights or motors .they are to protect. No set 
or group of incandescent lamps requiring over 2,000 
watts must be dependent upon one cut-out. 

2. Switches must be placed between non-grounded side 
and lights and motors they are to protect. 



234 MODERN ELECTEICAL CONSTRUCTION. 

3. Must have all rails bonded at each joint with a con- 
ductor having a carrying capacity at least equivalent 
to No. 00 B. & S. gage annealed copper wire, and all 
rails must be connected to the outside ground return 
circuit by a not less than No. 00 B. & S. gage copper 
wire or by equivalent bonding through the track. All 
lighting and stationary motor circuits must be thor- 
oughly and permanently connected to the rails or to 
the wire leading to the outside ground return circuit. 
/. All pendant cords and portable conductors will be con- 
sidered as subject to hard usage (see 45-/). 

g. Must, except as provided in Section e, have all wiring 
and apparatus installed in accordance with the rules for con- 
stant potential systems. 

h. Must not have any system of feeder distribution cen- 
tering in the building. 

i. Cars must not be left with the trolley in electrical con- 
nection wath the trolley wire. 

34. Lighting and Power from Railway Wires. 

a. Must not he permitted under any pretense, in the same 
eircuit with trolley mires with a ground return, except in elec- 
tric railway cars, electric car houses and their power stations, 
nor shall the same dynamo he used for hoth purposes. 



HIGH-POTENTIAL SYSTEMS. 

550 TO 3,500 Volts. 

Any circuit attached to any machine or comhination of ma- 
chines which develops a difference of potential, hetween 
any tzvo zvires, of over 550 volts and less than 3,500 volts, 
shall he considered as a high-potential circuit, and as 
coming under that class, unless an approved transforming 
device is used, which cuts the difference of potential 
down to 330 volts or less. 

(See note following first paragraph under Low-Potential 
systems. 



HIGH POTENTIAL SYSTEMS. 235 

35. Wires. 

(See also Nos. 14, 75 and 16.) 

a. Must have an approved rubber-insulating covering 
(see No. 41). 

h. Must be always in plain sight and never encased, ex- 
cept as provided for in No. 8 h, or where required by the In- 
spection Department having jurisdiction. 

c. Must (except as provided for in No. 8 h), be rigidly 
supported on glass or porcelain insulators, which raise the 
wire at least one inch from .the surface wired over, and must 
be kept about eight inches apart. 

Rigid supporting- requires, under ordinary conditions, where 
wiring along flat surfaces, supports at least about every four 
and one-half feet. Tf the wires are unusually liable to be 
disturbed, the distance between supports should be shortened. 

In buildings of mill construction, mains of No. 8 B. & S. 
gage or over, where not liable to be disturbed, may be sep- 
arated about ten inches and run from timber to timber, not 
breaking around, and may be supported at each timber only. 

d. Must be protected on side walls from mechanical 
injury by a substantial boxing, retaining an air space of one 
inch around the conductors, closed at the top (the wires 
passing through bushed holes) and extending not less than 
seven feet from the floor. When crossing floor timbers, in 
cellars, or in rooms where they might be exposed to injury 
wires must be attached by their insulating supports to the 
under side of a wooden strip not less than one-half an inch in 
thickness. 

For general suggestions on protection, see note under 
No. 24 e. See also note under No. 18 e. 

36. Transformers. (When permitted mside buildings, see 

No. 13.) 

(For construction rules, see No. 62.) 
(See also Nos. 13 and 13 A.) 

Transformers must not be placed inside of buildings with- 
out special permission from the Inspection Department having 
jurisdiction. 



236 MODEKN ELECTRICAL CONSTKUCTION. 



a. Must be located as near as possible to the point at 
which the primary wires enter the building. 

b. Must be placed in an enclosure constructed of fire- 
resisting material ; the enclosure to be used only for this pur- 
pose, and to be kept securely locked, and access to the same 
allowed only to responsible persons. 

c. Must be thoroughly insulated from the ground, or 
permanently and effectually grounded, and the enclosure in 
which they are placed must be practically air-tight, except 
that it must be thoroughly ventilated to the out-door air, if 
possible, through a chimney or flue. There should be at 
least six inches air space on all sides of the transformer. 

37. Series Lamps. 

a. No multiple series or series multiple system of light- 
ing will be approved. 

b. Must not, under any circumstances, be attached to gas 
fixtures. 



EXTRA-HIGH-POTENTIAL SYSTEMS. 

Over 3,500 Volts. 

Any circuit attached to any machine or combination of ma- 
chines zvhich develops a difference of potential, between 
any tzvo zvires, of over 3.500 volts, shall be considered as 
an extra-high-pofential circuit, and as coming under that 
class, unless an approved transforming device is used, 
zvhich cuts the difference of potential dozvn to 3,500 volts 
or less. 

38. Primary Wires. 

a. IMust not be brought into or over buildings, except 
power stations and sub-stations. 



EXTRA HIGH POTENTIAL SYSTEMS. 237 

39. Secondary Wires. 

a. Must be ins.talled under rules for high-potential sys- 
tems when their immediate primary wires carry a current at 
a potential of over 3,500 volts, unless the primary wires are 
installed in accordance with the requirements as given in 
rule 12 A or are entirely underground, within city, town and 
village limits. 



NOTICE— DO NOT FAIL TO SEE WHETHER ANY 
RULE OR ORDINANCE OF YOUR CITY CONFLICTS 
WITH THESE RULES. 



Class D. 

FITTINGS, MATERIALS AND DETAILS OF 
CONSTRUCTION. 

(Light, Power and Heat. For Signaling Systems see 

Class E.) 



ALL SYSTEMS AND VOLTAGES. 

The following rules are hut a partial outline of require- 
ments. Devices or material zvhich fulfill the conditions of 
these requirements and no more will not necessarily be ac- 
ceptable. All fittings and materials should be submitted for 
examination and test before bring introduced for use. 

INSULATED WIRES— Rules 40 to 48. 



40. General Rules. 

a. Copper for insulated solid conductors of No. 4 B. & 
S. gage and smaller must not vary in diameter more than 
.002 of an inch from the standard. On solid sizes larger than 
No. 4 B. & S. gage the diameter shall not vary more than one 
per cent from the specified s.tandard. The conductivity of 
solid conductors shall not be less than 97% of that of pure 
copper of the specified size. 

In all stranded conductors the sum of the circular mils of 
the individual wires shall not be less than the nominal cir- 
cular mils of the strand by more than one and one-half per 



FITTINGS^ MATERIALS, ETC. 239 

cent. The conductivity of the individual wires in a strand 
shall not be less than is given in the following table: 

Number Per cent 

14 and larger 97.0 

15 96.8 

16 96.6 

17 96.4 

18 96.2 

19 96.0 

20 95.8 

21 95.6 

22 95.4 

23 95.2 

24 95.0 

25 94.8 

26 94.6 

27 94.4 

28 94.2 

29 94.0 

30 93.8 

The Standard for diameters and mileages shall be that 
adopted by the American Institute of Electrical Engineers. 

b. Wires and cables of all kinds designed to meet the 
following specifications must have a distinctive marking the 
entire length of the coil, so that they may be readily identi- 
fied in the field. They must also be plainly tagged or marked 
as follows : 

1. The maximum voltage at which the wire is designed 

to be used. 

2. The words "National Electrical Code Standard." 

3. Name of the mianufacturing company and, if desired, 

trade name of the w^ire. 

4. Month and year when manufactured. 

Wires described under Nos. 42, 43 and 44 need not have 
the distinctive marking, but are to be tagged. 

41. Rubber-Covered Wire. 

a. Copper for conductors must be thoroughly tinned. 
Insulation for Voltages, to 600 inclusive. 

b. Must be of rubber or other approved substances. 



240 MODERN ELECTRICAL CONSTRUCTION. 

homogeneous in character, adhering to the conductor and of 
a thickness not less than that given in the following table : 
B. & S. Gage. Thickness. 

18 to 16 1-32 inch 

15 to 8 3-64 

7 to 2 1-16 

1 to 0000 5-64 

Circular Mils. 

250,000 to 500,000 3-32 

500,000 to 1,000,000 7-64 

Over 1,000,000 1-8 

Measurements of insulating wall are to be made at the 
thinnest portion of the dielectric. 

c. The completed coverings must show an insulation re- 
sistance of at least 100 megohms per mile during thirty days' 
immersion in water at 70 degrees Fahrenheit (21 degrees 
Centigrade). 

d. Each foot of the completed covering must show a 
dielectric strength sufficient to resist throughout five minutes 
the application of an electro-motive force proportionate to 
the thickness of insulation in accordance with the following 
table : 

Thickness Breakdown Teat 

in 64th inches. on 1 foot. 

1 3,000 Volts A. C. 

I 6,000 

5 9,000 
4 11,000 

6 13,000 

6 15,000 

7 16,500 

8 18,000 
10 21.000 
12 . 23,500 
14 26,000 
16 28,000 

The source of alternating electro-motive force shall be a 
transformer of at least one kilowatt capacity. The application 
of the electro-motive force shall first be made at 4,000 volts 
for five minutes and then the voltage increased by steps of not 
over 3,000 volts, each held f©r five minutes, until the rupture 
of the insulation occurs. The test for dielectric strength shall 
be made on a sample of wire which has been immersed in 



FITTINGS, MATERIALS, ETC. ^41 

water for seventy-two hours. One foot of wire under test 
is to be submerged in a conducting liquid held in a metal 
trough, one of the transformer terminals being connected to 
the copper of the wire and the other to the metal of the 
trough. 

Insulations for Voltages between 600 and 3,500. 

e. The thickness of the insulating wall must not be less 
than that given in the following table : 

B. & S. Gage. Thickness. 

14 to 1 3-32 inch. 

to 0000 3-32 inch, covered by tape or braid. 

Circular Mils. 

250.000 to 500,000 3-32 Inch, covered by tape or braid. 

Over 500,000 1-8 inch, covered by tape or braid. 

f. The requirements as to insulation and break-down re- 
sistance for wires for low-potential systems shall apply, with 
the exception that an insulation resistance of not less than 
300 megohms per mile shall be required. 

Insulation for Voltage over 3,500. 

g. Wire for arc-light circuits exceeding 3,500 volts poten- 
tial must have an insulating wall not less than three-six- 
teenths of an inch in thickness, and shall withstand a break- 
down test of at least 23,500 volts and have an insulation of 
at least 500 megohms per mile. 

The tests on this wire to be made under the same condi- 
tions as for low-potential wires. 

Specifications for insulations for alternating currents ex- 
ceeding- 3,500 volts have been considered, but on account of the 
somewhat complex conditions in such work it has so far been 
deemed Inexpedient to specify general insulations for this use. 

General. 

h. The rubber compound or other approved substance 
used as insulation must be sufficiently elastic to permit all 
wires smaller than No. 7 B. & S. gage and larger than No. 
11 B. & S. gage to be bent without injury to the insulation 



242 MODERN ELECTRICAL CONSTRUCTION. 

around a cylinder twice the diameter of the insulated wire 
measured over the outer covering. All wires No. 11 B. & S. 
gage and smaller to be bent without injury to the insulation 
around a cylinder equal to the diameter of the insulated wire 
measured over .the outer covering. 

/. All of the above insulations must be protected by a 

substantial braided covering, properly saturated with a . pre- 

• servative compound. This covering must be sufficiently 

strong to withstand all the abrasion likely to be met with in 



Figure 138. 

practice, and must substantially conform to approved sam- 
ples submitted by the manufacturer. 

42. Slow-burning Weatherproof Wire. 

(See Figure 138.) 

This wire Is not a^s burnable as "weatherproof" nor as 
subject to softening- under heat. It is not suitable for outside 
work. 

a. The insulation must consist of two coa.tings, one to be 
fireproof in character and the other to be weatherproof. The 
fireproof coating must be on the outside and must comprise 
about six-tenths of the total thickness of the wall. The com- 
pleted covering must be of a thickness not less than that given 
in the following table : 

B. & S. Gage. Thickness. 

14 to 8 3-64 inch 

7 to 2 1-16 " 

1 to 0000 5-64 " 

Circular Mils. 

250,000 to 500,000..., 3-32 " 

500,000 to 1,000,000 7-64 " 

Over 1,000,000 1-8 ** 

Measurements of insulating wall are to be made at the 
thinnest portion of the dielectric. 

b. The fireproof coating shall be of the same kind as that 



FITTINGS, MATEEIALS, ETC. 243 

required for "slow-burning wire," and must be finished witli a 
hard, smooth surface. 

c. The weatherproof coating shall consist of a stout 
braid, applied and treated as required for "weatheroroof 
wire." 

43. Slow-burning Wire. 

a. The insulation must consist of three braids of cotton 
or other thread, all the interstices of which must be filled 
with the fireproofing compound or with material having 
equivalent resisting and insulating properties. The outer 
braid m.ust be specially designed to withstand abrasion, and 



Figure 139. 

its surface must be finished smooth and hard. The com- 
pleted covering must be of a thickness not less than that 
given in the table under No. 42 a. 

The solid constituent of the fireproofing" compound must 
not be susceptible to moisture, and must not burn even when 
ground in an oxidizable oil, making- a compound which, while 
proof against fire and moisture, at the same time has consider- 
able elasticity, and which when dry will suffer no change at a 
temperature of 250 degrees Fahrenheit (121 degrees Centi- 
grade), and which will not burn at even a higher temperature. 
This is practically the old so-called "underwriters" insula- 
tion. It is especially useful in hot, dry places where ordinary 
insulations would perish, and where wires are bunched, as on 
the back of a large switchboard or in wire tower, so that 
the accumulation of rubber insulation would result In an 
objectionably large mass of highly inflammable material. 

44. Weatherproof Wire. 

(See Figure 139.) 

a. The insulating covering shall consist of at least three 
braids, all of which must be thoroughly saturated with a dense 
moisture-proof compound, applied in such a manner as to 
drive any atmospheric moisture from the cotton braiding, 



244 MODERN ELECTKICAL CONSTRUCTION. 

thereby securing a covering to a great degree waterproof and 

of high insulating power. This compound must retain its 

elasticity at deg. Fahr. and must not drip at 160 deg. Fahr. 

The thickness of insulation must not be less than that given 

in the table No. 42 A, and the outer surface must be 

thoroughly slicked down. 

This wire is for use outdoors, where moisture is certain and 
where fireproof qualities are not necessary. 

45. Flexible Cord. 

(For installation rules, see No. 28.) 

a. Must, except as required for portable heating ap- 
paratus (see section g), be made of stranded copper con- 
ductors, each strand to be not larger than No. 26 or smaller 




Figrure 140. 

than No. 30 B. & S. gage, and each stranded conductor must 
be covered by an approved insulation and protected from me- 
chanical injury b}' a tough, braided outer covering. 

For Pendant Lamps. 

(See Figure 140.) 

In this class is to be included all flexible cord which, under 
usual conditions, hangs freely in air, and which is not likely 
to be moved sufficiently to come in contact with surrounding 
objects. 

It should be noted that pendant lamps provided with long 
cords, so that they can be carried about or hung over nails or 
on machinery, etc., are not included in this class, even though 
they are usually allowed to hang freely in air. 

b. Each stranded conductor must have a carrying capacity 
equivalent to not less* than a No. 18 B. & S. gage wire 

e. The covering of each stranded conductor must be made 
up as follows : 

1. A tight, close wind of fine cotton. 

2. The insulation proper, which shall be waterproof. 



FITTINGS, MATERIALS, ETC. 245 

3. An outer cover of silk or cotton. 

The wind of cotton tends to prevent a broken strand punc- 
turing- the insulation and causing a short circuit. It also keeps 
the rubber from corroding the copper. 

d. The insula.tion must be solid, at least one thirty-second 
of an inch thick, and must show an insulation resistance of 
fifty megohms per mile throughout two weeks' immersion in 
water at 70 degrees Fahrenheit, and stand the tests prescribed 
for low-tension wires as far as they apply. 

e. The outer protecting braiding should be so put on and 
sealed in place that when cut it will not fray out and where 
cotton is used it should be impregnated with a flameproof 
paint, which will not have an injurious effect on the insula- 
tion. 

For Portables. 

(See Figure 141.) 
In this classi is included all cord used on portable lamps, 
small portable motors, or any device which is liable to be 
carried about. 

/. Flexible cord for portable use except in offi'ces, dwell- 
ings or similar places, where cord is not liable to rough usage 
and where appearance is an essential feature, must meet all 
the requirements for flexible cord for "pendant lamps," both 




Figure 141. 

as to construction and thickness of insulation, and in addi- 
tion mus.t have a tough braided cover over the whole. There 
must also be an extra layer of rubber between the outer 
cover and the flexible cord, and in moist places the outer 
cover must be saturated with a moisture-proof compound, 
thoroughly slicked down, as required for ''weatherproof wire" 
in No. 44. In offices, dwellings, or in similar places where 
cord is not liable to rough usage and where appearance is an 
essential feature, flexible cord for portable use must "meet all 
of the requirements for flexible cord for "pendant lamps," 



24G MODEUN ELECTKICAL CONSTRUCTION. 

both as to construction and thickness of insulation, and in ad- 
dition must have a tough, braided cover over the whole, or 
providing there is an ex.tra la3'er of rubber between the 
flexible cord and the outer cover, the insulation proper on 
each stranded conductor of cord may be 1-64 of an inch in 
thickness instead of 1-32 of an inch as required for pendant 
cords. 

Flexible cord for portable use may, instead of the outer 
covering's described above, have an approved metal flexible 
armor. 

For Portable Heating Apparatus. 

(See Figure lk2.) 

Applies to all smoothing and sad irons and to any other 
device requiring over 250 watts. 

g. Must be made as follows : 

1. Conductors must be of braided copper, each strand 

not to be larger than No. 30 or smaller than No. 36 

B. & S. gage. 

When conductors have a greater carrying capacity than 
No. 12 B. & S. gage they may be braided or stranded 
with each strand as large as No. 28 B. & S. gage. If 
stranded there must be a tight, close wind of cotton 
between the conductor and the insulation. 




Figure 142. 

2. An insulating covering of rubber or other approved 

material not less than one sixty-fourth inch in thick- 
ness. 

3. A braided covering of not less than one thirty-second 

inch thick, composed of best quality long fiber as- 
bestos, containing not over 5 per cent of vegetable 
fiber. 

4. The several conductors comprising the cord to be en- 

closed by an outer reinforcing covering not less than 
one sixty-fourth inch thick, especially designed to 
resist abrasion, and so treated as to prevent the 
cover from fraying. 



FITTINGS, MATERIALS, ETC. 247 

46. Fixture Wire. 

{See Figure 14J.) 

(For installation rules, see No. 24 v to y.) 

a. May be made of solid or stranded conductors, with 

no strands smaller than No. 30 B. & S. gage, and must have 

a carrying capacity not less than that of a No. 18 B. & S. 

gage wire. 

h. Solid conductors must be thoroughly tinned. If a 
stranded conductor is used, it must be covered by a tight, 
close wind of fine cotton. 

r. Must have a solid rubber insulation of a thickness not 
less than one thirty-second of an inch for Nos. 18 to 16 B. 
& S. gage, and three sixty-fourths of an inch for Nos. 14 to 
8 B. & S. gage, except that in arms of fixtures not exceeding 
twenty-four inches in length and used to supply not more than 
one sixteen-candle-power lamp or its equivalent, which are 

Figure 143. 

so constructed as to render impracticable the use of a wire 
with one thirty-second of an inch thickness of rubber insula- 
tion, a thickness of one sixty-fourth of an inch will be permit- 
ted. 

d. Must be protected with a covering at least one sixty- 
fourth of an inch in thickness, sufficiently tenacious to with- 
stand the abrasion of being pulled into the fixture, and suf- 
ficiently elastic to permit the wire to be bent around a 
cylinder with twice the diameter of the wire without in- 
jury .to the braid. 

e. Must successfully withstand the tests specified in Nos. 

41 c and 41 d. 

In wiring certain designs of show-case fixtures, ceiling 
bulls-eyes and similar appliances in which the wiring is 
exposed to temperatures in excess of 120 degrees Fahrenheit 
(49 degrees Centigrade), from the heat of the lamps, slow- 
burning wire may be used (see No. 43). All such forms of 
fixtures must be submitted for examination, test and approval 
before being introduced for use. 



248 MODEIiN ELECTiaCAL CONSTRUCTION. 

47. Conduit Wire. 

(For installation rules, see No. 24 n. to p.) 

a. Single wire for lined conduits must comply with the 
requirements of No. 41 (Figure 144). For unlined con- 
duits it must comply with the same requiremeats — except that 



Figure 144. Figure 145. Figure 146. 

tape may be substituted for braid — and in addition there must 
be a second outer fibrous covering, at least one thirty-second 
of an inch in thickness and sufficiently tenacious to with- 
stand the abrasion of being hauled through the metal con- 
duit (Figures 145 and 146). 

b. For twin or duplex wires in lined conduit, each con- 
ductor must comply with the requirements of No. 41 — except 
that tape may be substituted for braid on the separate con- 
ductors — and must have a substantial braid covering the 
whole. For unlined conduit, each conductor must comply 
with requirements of No. 41 — except that tape may be sub- 
stituted for braid — and in addition must have a braid covering 
the whole, at least one thirty-second of an inch in thick- 
ness and sufficiently tenacious to withstand the abrasion of 
being hauled through the metal conduit (Figure 147). 

c. For concentric wire, the inner conductor must comply 
with the requirements of No. 41 — except that tape may be 




Figure 147. Figure 148. 

substituted for braid — and there must be outside of the outer 
conductor the same insulation as on the inner, the whole to be 
covered with a substantial braid, which for unlined conduits 
must be at least one thirty-second of an inch in thickness, and 
sufficiently tenacious to withstand the abrasion of being 
hauled through the metal conduit. (Figure 148). 



FITTINGS, MATERIALS, ETC. 



249 



The braid or tape required around each conductor in duplex, 
twin and concentric cables is to hold the rubber insulation In 
place and prevent jamming- and flattening-. 

All the braids specified in this rule must be properly sat- 
urated with a preservative compound. 

48. Armored Cable. 

(See Figure 149.) 
(For installation rules , see N'o. 24A.) 

a. The armor of such cables must have at least as great 
strength to resist penetration of nails, etc., as is required for 




m%MM 



Figure 149. 




metal conduits (see No. 49 h), and its thickness must not be 
less than that specified in the following table : 



Nominal 


Actual 


Actual 




Internal 


Internal 


External 


Thickness 


Diameter. 


Diameter. 


Diameter. 


of Wall. 


Inches. 


Inches. 


Inches. 


Inches. 


Vs 


.27 


.40 


.06 


¥4 


.36 


.54 


.08 


% 


.49 


.67 


.09 


V2 


.62 


.84 


.10 


% 


.82 


1.05 


.11 


1 


1.04 


1.31 


.13 


IV4 


1.38 


1.66 


.14 


11/^ 


1.61 


1.90 


.14 


2 


2.06 


2.37 


.15 


214 


2.46 


2.87 


.20 


3 


3.06 


3.50 


.21 


SVa 


3.54 


4.00 


.22 


4 


4.02 


4.50 


.23 


4y2 


4.50 


5.00 


.24 


5 


5.04 


5.56 


.25 


• 


6.06 


6.62 


28 



250 MODERN ELECTRICAL CONSTRUCTION. 

An allowance of two one-hundredths of an inch for variation 
in manufacturing- and loss of thickness by cleaning- will be 
permitted. 

b. The conductors in same, single wire or twin conduc- 
tors, must have an insulating covering as required by No. 41 ; 
if any filler is used to secure a round exterior, it must be im- 
pregnated with a moisture repellent, and the whole bunch of 
conductors and fillers must have a separate exterior covering. 

49. Interior Conduits. 

(For installation rules, see Nos. 24 n to p and 25.) 

a. Each length of conduit, whether lined or unlined, must 
have the maker's name or initials stamped in the nictal or at- 
tached thereto in a satisfactory manner, so that inspectors can 
readily see the same. 

The use of paper stickers or tags cannot be considered 
satisfactory methods of marking, as they are readily loosened 
and lost off in the ordinary handling of the conduit. 

Metal Conduits with Lining of Insulating Material. 

(See Figure 150.) 

b. The metal covering or pipe must be at least as strong 
as the ordinary commercial forms of gas pipe of the same 




Figure 150. 

size, and its thickness must be not less than that of standard 
gas pipe as specified in the table given in No. 48. 

c. Must not be seriously affected externally by burning 
out a wire inside the tube when the iron pipe is connected to 
one side of the circuit. 

d. Must have the insulating lining firmly secured to the 
pipe. 

e. The insulating lining must not crack or break when a 
length of the conduit is uniformly bent at temperature of 212 



FITTINGS, MATERIALS, ETC. 251 

degrees Fahrenheit to an angle of ninety degrees, with a curve 
having a radius of fifteen inches, for pipes of one inch and 
less, and fifteen times .the diameter of pipe for larger sizes. 

/. The insulating lining must not soften injuriously at a 
temperature below 212 degrees Fahrenheit and must leave 
water in which it is boiled practically neutral. 

g. The insulating lining must be at least one thirty-second 
of an inch in thickness. The materials of which it is com- 
posed must be of such a nature as will not have a deteriorat- 
ing effect on the insulation of the conductor and be suffi- 
ciently tough and tenacious to withstand the abrasion test 
of drawling long lengths of conductors in and out of same. 

It. The insulating lining must no.t be mechanically weak 
after three days' submersion in water, and when removed 
from the pipe entire must not absorb more than ten per 
cent of its weight of water during 100 hours of submersion. 

i. All elbows or bends must be so made that the con- 
duit or lining of same will not be injured. The radius of the 
curve of the inner edge of any elbow must not be less than 
three and one-half inches. 

Unlined Metal Conduits. 

{See Figure i^i.) 
j. Pipe sizes to run as follows : 



Trade Size. 


Approximate Internal 


Minimum Thickness 


Inches. 


Diameter. 


of Wall. 




Inches. 


Inches. 


V2 


.62 


.100 


% 


.82 


.105 


1 


1.04 


.125 


ly* 


1.38 


.135 


1V2 


1.61 


.140 


2 


2.06 


.150 


2y2 


2.46 


.200 


3 


3.06 


.210 


3Vo 


3.54 


.220 



At no point (except at screw thread) shall the thickness of 
wall of finished conduit be less than the minimum specified 
in last column of above table. 

k. Pipe to be thoroughly cleaned to remove all scale. 



252 



MODERN ELECTRICAL CONSTRUCTION. 



Pipe should be of sufficiently true circular section to admit 
of cutting true, clean threads, and should be very closely the 
same in wall thickness at all points with clean square weld. 




Figure 151. 



/. Cleaned pipe to be protected against effects of oxida- 
tion, by baked enamel, zinc or other approved coating which 
will not soften at ordinary temperatures, and of sufficient 
weight and toughness to successfully withstand rough usage 
likely to be received during shipment and installation ; and 




Figure 152. 



of sufficient elasticity to prevent flaking when !^ inch con- 
duit is bent in a curve the inner edge of which has radius 
of Zy2 inches. 

m. All elbows or bends must be so made that the con- 
duit will not be injured. The radius of the curve of the 
inner edge of any elbow not to be less than 3j^ inches. 

49 A. Switch and Outlet Boxes. 

(See Figure IJ2.) 

a. Must be of pressed steel having a wall thickness not 



FITTINGS, MATERIALS, ETC. 253 

less than .081 in. (No. 12 B. & S. gage) or of cast metal 
having a wall thickness not less than 0.128 in. (No. 8 B. & 
S. gage.) 

b. Must be well galvanized, enameled or otherwise prop- 
erly coated, inside and out, to prevent oxidation. 

c. Must be so made that all openings not in use will be 
effectively closed by metal which will afford protection sub- 
stantially equivalent to^the walls of the box. 

d. Must be plainly marked, where it may readily be 
seen when installed, with the name or trade mark of the 
manufacturer. 

e. Must be arranged to secure in position the conduit or 
flexible tubing protecting the wire. 

This rule will be complied with if the conduit or tubing 
is firmly secured in position by means of some approved device 
which may or may not be a part of the box. 

f. Boxes used with lined conduit must comply with the 
foregoing requirements, and in addition must have a tough 
and tenacious insulating lining at least 1-32 inch thick, firmly 
secured in position. 

g. Switch and outlet boxes must be so arranged that they 
can be securely fastened in place independently of the sup- 
port afforded by the conduit piping, except that when entirely 
exposed, approved boxes, which are threaded so as to be 
firmly supported by screwing on to the conduit pipe, may 
be used. 

h. Switch boxes must completely enclose the switch on 
sides and back and must provide a thoroughly substantial 
support for it. The retaining screws for the box must not 
be used to secure the switch in position. 

i. Covers for outlet boxes must be of metal equal in 
thickness to that specified for the walls of the box, or must 
be of metal lined with an insulating material not less than 
1-32 inch in thickness, firmly and permanently secured to*the 
metal. 



254 



MODERN ELECTRICAL CONSTRUCTION. 



50. Mouldings. 

(For wiring rules, see No. 24 k to m.) 

Wooden Mouldings. 

a. Must have, both outside and inside, at least two coats 
of waterproof material, or be impregnated with a moisture 
repellent. 

b. Must be made in two pieces, a backing and a capping 
and must afford suitable protection from abrasion. Must be 
so constructed as to thoroughly encase the wire, be provided 
with a tongue not less than 1-2 inch in thickness between the 




Figure 153. 



conductors, and have exterior walls which under grooves shall 
not be less than 3-8 inch in thickness, and on the sides not 
less than 1-4 inch in thickness. 

It is recommended that only hardwood moulding be used. 

Metal Mouldings. 

(For zanring rules, see Nos. 24, k to m, and 2S A.) 

e. Each length of such moulding must have maker's name 
or trade mark stamped in the metal, or in some manner per- 
majiently attached thereto, in order that it may be readily 
identified in the field. 

The use of paper stickers or tags cannot be considered 



FITTINGS, MATERIALS, ETC. 255 

satisfactory methods of marking-, as they are readily loosened 
and lost off in ordinary handling of the moulding. 

d. Must be constructed of iron or steel with backing at 
least .050 inch in thickness, and with capping not less than 
,040 inch in thickness, and so constructed that when in place 
the raceway will be entirely closed; must be thoroughly gal- 
vanized or coa.ted with an approved rust preventive both 
inside and out to prevent oxidation. 

e. Elbows, couplings and all other similar fittings must 
be constructed of at least the same thickness and quality of 
metal as the moulding itself and so designed that they will 
both electrically and mechanically secure the different sec- 
tions together and maintain the continuity of the raceway. 
The interior surfaces must be free from burrs or sharp cor- 
ners which might cause abrasion of the wire coverings. 

/. Must at all outlets be so arranged that the conductors 
cannot come in contact with the edges of the metal, either 
of capping or backing. Specially designed tittings which will 
interpose substantial barriers between conductors and the 
edges of metal are recommended. 

g. When backing is secured in position by screws or 
bolts from the inside of the raceway, depressions must be pro- 
vided to render the heads of the fastenings flush with the 
moulding. 

h. * Metal mouldings must be used for exposed work only 
and must be so constructed as to form an open raceway to 
be closed by the capping or cover after the wires are laid in. 

50A. Tubes and Bushings. 

(See Figure 153.) 

a. Construction. — Must be made straight and free from 
checks or rough projections, with ends smooth and rounded 
to facilitate the drawing in of the wire and prevent abrasion 
of its covering. 

h. Material and Test. — Must be made of non-combust- 
ible insulating material, which, when broken and submerged 
for 100 hours in pure water at 70 degrees Fahrenheit, will 
not absorb over one-half of one per cent of its weight. 



Diameter 


External 


of 


Diameter, 


Hole. 




Inches. 


Inches. 


1% 


^ 


% 


H 


V2 


if 


% 


H 


% 


lA 


1 


W^ 


IV4 


m 


1% 


2^ 


1% 


2^ 


2 


2if 


2*4 


3^ 


2y2 


3H 



256 MODERN ELECTRICAL CONSTRUCTION. 

c. Marking. — Must have the name, initials or trade 
mark of the manufacturer stamped in the ware. 

d. Sizes. — Dimensions of walls and heads must be at 
least as great as those given in the following table: 

Thick- External Length 

ness of Diameter of 

Wall. of Head. Head. 

Inches. Inches. Inches. 

% M V2 

A \i V2 

A li^ V2 

A 1^ % 

/u IH % 

/j lit % 

A 2^ % 

hh m % 

M 3tV % 

M 3f^ % 

H 3if 1 

M 4^ 1 

An allowance of one-sixty-fourth of an inch for variation 

In manufacturing" will be permitted, except in the thickness of 

the wall. 

SOB. Cleats. 

(See Figure 153.) 

a. Construction. — Must hold the wire firmly in place 
without injury to its covering. 

Sharp edg-es which may cut the wire should be avoided. 

h. Supports. — Bearing points on the surface must be 
made by ridges or rings about the holes for supporting screws, 
in order to avoid cracking and breaking when screwed tight. 

c. Material and Test. — Must be made of non-combust- 
ible insulating material, which, when broken and submerged 
for 100 hours in pure water at 70 degrees Fahrenheit, will 
not absorb over one-half of one per cent of its weight. 

d. Marking. — Must have the name, initials or trade 
mark of the manufaciurer stamped in the ware. 

e. Sizes. — Must conform to the spacings given in the 
following table: 

Distance from Wire Distance between 
Voltag-e to Surface. Wires. 

0-300 % inch. 2% Inches. 



FITTINGS, MATERIALS, ETC. 257 

This rule will not be interpreted to forbid the placing of the 
neutral of an Edison three-wire system in the center of the 
three-wire cleat where the difference of potential between the 
outside wires is not over 300 volts, provided the outside wires 
are separated two and one-half inches. 

50C. Flexible Tubing. 

(See Figure 154.) 

a. Must have a sufficiently smooth interior surface to 
allow the ready introduction of the wire. 

h. Must be constructed of or treated with materials 
which will serve as moisture repellents. 

c. The tuba must be so designed that it will withstand 
all the abrasion likely to be met with in practice. 

d. The linings, if any, must not be removable in lengths 
of over three feet. 

e. The 1-4 inch tube must be so flexible that it will not 
crack or break when bent in a circle with 6-inch radius at 
50 degrees Fehrenheit (10 degrees Centigrade), and the cov- 
ering must be thoroughly saturated with a dense moisture- 




Figure 154, 



proof compound which will not slide at 150 degrees Fahren- 
heit (65 degrees Centigrade). Other sizes must be as well 
made. 

f. Must not convey fire on the application of a flame from 
Bunsen burner to the exterior of the tube when held in a 
vertical position. 

g. Must be sufficiently tough and tenacious to withstand 
severe tension without injury; the interior diameter must not 
be diminished or the tube opened up at any point by the 
application of a reasonable stretching force. 

h. Must not close to prevent the insertion of the wire 
after the tube has been kinked or flattened and straightened 
out. 



258 



MODERN ELECTRICAL CONSTRUCTION. 



51. Switches. 

(For installation rules, see Nos. 17 and 22!) 

General Rules. 

a. Must, when used for service switches, indicate, on in- 
spection, whether the current be "on" or ''oflf." 

h. Must, for constant-current systems, close the main cir- 
cuit and disconnect the branch wires when turned "off" ; must 
be so constructed that they shall be automatic in action, not 
stopping between points when started, and must prevent an 
arc between the points under all circumstances. They must 
indicate whether the current be "on" or "off." 



Knife Switches. 
(See Figure 135.) 

Knife switches must be made to comply with the following 
specifications, except in those few cases where peculiar design 
allows the switch to fulfill the general requirements in some 
other way, and where it can successfully withstand the test 
of Section i. In such cases, the switch should be submitted 
for special examination before being used. 

c. Base. — Must be mounted on non-combustible, non- 
absorptive insulating bases, such as slate or 

porcelain. Bases with an area of over twenty 
five square inches must have at least four sup- 
porting screws. Holes for the supporting 
screws must be so located or countersunk that 
there will be at least one-half inch space, meas- 
ured over the surface, between the head of 
the screw or washer and the nearest live metal 
part, and in all cases when between parts of 
opposite polarity must be countersunk. 

d. Mounting. — Pieces carrying the con- 
tact jaws and hinge clips must be secured to 
the base by at least two screws, or else made 
with a square shoulder or provided with dowel- 
pins, to prevent possible turnings, and the nuts 
or screw heads on the under side of the base 
must be countersunk not less than one-eighth 




Fig. 155. 



FITTINGS, MATERIALS, ETC. 259 

inch and covered with a waterproof compound which will not 
melt below 150 degrees Fahrenheit. 

e. Hinges. — Hinges of knife switches must jx)t be used 
to carry current unless they are equipped with spring washers, 
held by lock-nuts or pins, or their equivalent, so arranged that 
a firm and secure connection will be maintained at all posi- 
tions of the switch blades. 

Spring washers must be of sufficient strength to take up 
any wear in the hinge and maintain a good contact at all 
times. 

/. Metal. — All switches must have ample metal for 
stiffness and to prevent rise in temperature of any part of over 
fifty degrees Fahrenheit at full load, the contacts being ar- 
ranged so that a thoroughly good bearing at every point is 
obtained with contact surfaces advised for pure copper blades 
of about one square inch for each seventy-five amperes ; the 
whole device must be mechanically well made throughout. 

g, Cross-Bars. — All cross-bars less than three inches 
in length must be made of insulating material. Bars of three 
inches and over, which are made of metal, to insure greater 
mechanical strength, must be sufficiently separated from the 
jaws of the switch to prevent arcs following from the con- 
tacts to the bar on the opening of the switch under any cir- 
cumstances. Metal bars should preferably be covered with 
insulating material. 

To prevent possible turning or twisting the cross-bar must 
be secured to each blade by two screws, or the joints made 
with square shoulders or provided with dowel-pins. 

h. Connections. — Switches for currents of over thirty 

amperes must be equipped with lugs, firmly screwed or 

bolted to the switch, and into which the conducting wires 

shall be soldered. For the smaller sized switches simple 

clamps can be employed, provided they are heavy enough to 

stand considerable hard usage. 

Where lugs are not provided, a rugged double V groove 
clamp is advised. A set screw gives a contact at only one 
point, is more likely to become loosened, and is almost sure to 
cut into the wire. For the smaller sizes, a screw and washer 
connection with turned-up lugs on the switch terminal gives a 
satisfactory contact. ' 



260 



MODERN ELECTRICAL CONSTRUCTION. 



/. Test. — Must operate successfully at 50 per cent over- 
load in amperes and 25 per cent excess voltage, under the most 
severe conditions with which they are liable to meet in practice. 

This test is designed to g-ive a reasonable margin between 
the ordinary rating of the switcli and the breaking-down point, 
thus securing a switch wliich can always safely handle its nor- 
mal load. Moreover, there is enough leeway so that a moderate 
amount of overloading would not injure the switch. 

;. Marking. — Must be plainly marked where it will be 
visible, when the switch is installed, with the name of the 
maker and the current and voltage for which the switch is 
designed. 

Switches desigiied for use on Edison three-wire systems 
must be marked with both voltages, that is the voltage between 
the outside wires and the neutral, and also that between the 
outside wires, followed by the ampere rating and the words 
"three wire." (For example, "125-250 v. 30 a, three-wire.") 

k. Spacings. — Spacings must be at least as great as 
those given in the following table. The spacings specified are 
correct for switches to be used on direct-current systems, and 
can therefore be safely followed in devices designed for alter- 
nating currents. 

125 volts or less: 

Minimum Separation of Minimum 
Nearest Metal Parts of Break- 
Opposite Polarity. Distance. 
For Switchboards and Panel Boards — 

10 amperes or less % inch. 

11-30 amperes 1 

31-50 amperes 1 14 

For individual Switches — 

10 amperes or less 1 inch. 

11-30 " 114 " 

31-100 " IVo " 

101-300 " 214 " 

301-600 " 2% " 

601-1000 " 3 

126 to 250 volts: 
For all Switches — 

10 amperes or less li/^ inch. 

11-30 amperes 

31-100 " 

101-300 " 

301-600 " 

601-1000 " 



1% 

2% 
21/. 
2% 
3 



V2 inch. 

% " 



% inch. 
1 

114 " 
2 

21/2 " 
2% " 



IV4 inch. 

iy2 



2 

2% 

21/2 

2% 



FITTINGS, MATEIIIALS, ETC. 



261 



For 100 ampere switches and largrer, the above spacings 
for 250 volts direct current are also approved for 500 volts 
alternating current. Switches with these spacings intended 
for use on alternating-current systems with voltage above 250 
volts must be stamped "250-volt D. C," followed by the alter- 
nating current voltage for which they are designed, and the 
letters "A. C." 

For all Switches — 

10 amperes or less 3i/^ inch. 3 inch. 

11-35 amperes 4 " 3i/^ " 

36-iOO " 41/2 " 4 

Auxiliary breaks or the equivalent are recommended for 
switches designed for over 300 volts and less than 100 amperes, 
and will be required on switches designed for use in breaking 
currents greater than 100 amperes at a pressure of more than 
300 volts. 

For three-wire Edison systems the separations and breal^ 
distances for plain three-pole knife switches must not be less 
than those required in the abov^e table for switches designed 
for the voltage between the neutral and outside wires. 

Snap Switches. 
{See Figures 156 and 157.) 

Flush, push-button, door, fixture, and other snap switches 
used on constant-potential systems, must t)e constructed in 
accordance with the following specifications. 

/. Base. — Current-carrying parts must be mounted on 
non-combustible, non-absorptive insulating bases, such as slate 




Figure 156. 



or porcelain, and the holes for supporting screws should be 
countersunk not less than one-eighth of an inch. There must 
in no case be less than three sixty-fourths of an inch space 
between supporting screws and current-carrying parts. 

Sub-bases of non-combustible, non-absorptive insulating 



262 



MODERN ELECTRICAL CONSTRUCTION. 



material, which will separate the wires at least one-half of 
an inch from the surface wired over, must be furnished with 
all snap switches used in exposed or moulding work. 

m. Mounting. — Pieces carrying contact jaws must be 
secured to the base by at least two screws, or else made with 
a square shoulder, or provided with dowel-pins or otherwise 
arranged, to prevent possible turnings ; and the nuts or screw 
heads on the under side of the base must be countersunk not 
less than one-eighth inch, and .covered with a waterproof 
compound which will not melt below 150 degrees Fahrenheit. 

n. Metal. — All switches must have ample metal for 
stiffness and to prevent rise in temperature of any part of over 





Fig"ure 157. 

50 degrees Fahrenheit at full load, the contacts being arranged 
so that a thoroughly good bearing at every point is obtained. 
The whole device must be mechanically well made throughout. 
In order to meet the above requirements on temperature 
rise without causing- excessive friction and wear on current- 
carrying" parts, contact surfaces of from 0.1 to 0.15 square 
inch for each 10 amperes will be required, depending upon 
the metal used and the form of construction adopted. 

0. Insulating Material. — Any material used for insu- 
lating current-carrying parts must retain its insulating and 
mechanical strength when subject to continued use, and must 
not soften at a temperature of 212 degrees Fahrenheit. It must 
also be non-absorptive. 

p. Binding Posts. — Binding posts must be substantially 



FITTINGS, MATERIALS, ETC. 263 

made, and the screws must be of such size that the threads 
will not strip when set up tight. 

A set-screw is likely to become loosened and is almost 
sure to cut into the wire. A binding- screw, under the head 
of which the wive miay be clamped, and a terminal plate pro- 
vided with upturned lug's or some other equivalent arrang-e- 
ment, afford reliable contact. After July 1, 1908, switches 
with the set-screw form of contact will not be approved. 

q. Covers. — Covers made of conducting material, ex- 
cept face plates for flush switches, must be lined on sides and 
top with insulating, tough and tenacious material at least one- 
thirty-second inch in thickness, firmly secured so that it will 
not fall out with ordinary handling. The side lining must ex- 
tend slightly beyond the lower edge of the cover. 

r. Handle or Button. — The handle or button or any 
exposed parts must not be in electrical connection with the 
circuit. 

s. Test. — Must *'make" and "break" with a quick snap, 
and must not stop when motion has once been imparted by the 
button or handle. 

Must operate successfully at 50 per cent over-load in 
amperes and at 125 volt direct current, for all 125 volt or 
less switches, and at 250 volts direct current, for all 126 to 
250 volt switches under the most severe conditions which 
they are liable to meet in practice. 

When slowly turned ''on and off" at the rate of about two or 
three times per minute, while carrying the rated current at 
rated voltage, must ''make and break" the circuit six thousand 
times before failing. 

t. Marking. — Must be plainly marked, where it may 
be readily seen after the device is installed, with the name 
or trade mark of the maker and the current and voltage for 
which the switch is designed. 

On flush switches these markings may be placed on the 
back of the face plate or on the sub-plate. On other types 
they must be placed on the front of the cap, cover, or plate. 

Switches w^hich indicate whether the current is "on" or 
**off" are recommended. 



264 



MODERN ELECTRICAL CONSTIIUCTION. 



52. Cut-Outs and Circuit-Breakers. 

{See Figuj'c J ^8.) 
(For insfallation rules, see Nos. ly and 21.) 

These requirements do not apply to rosettes, attaehmeni 
plugs, ear lighting cut-outs and protective devices for signal- 
ing systems. 

General Rules. 

a. Must be supported on bases of non-combustible, non- 
absorptive insulating material. 

h. Cut-outs must be of plug or cartridge type, when not 
arranged in approved cabinets, so as to obviate any danger of 
the melted fuse metal coming in contact with any substance 
which might be ignited thereby. 

c. Cut-outs must operate successfully on short-circuits, 
under the most severe conditions with which they are liable to 




^gle Pole. 



Double Pole. 



Figure 158. 



meet in practice,' at 25 per cent above their rate of voltage and 

the fuses rated at 50 per cent above the current for which the 

cut-out is designed, and for enclosed fuse cut-outs with the 

largest fuses for which the cut-out is designed. 

With link fuse cut-outs there is always the possibility of 
a larg-er fuse being put into the cut-out than it was designed 



FITTINGS, MATBKIALS, ETC. 265 

for, which is not true of enclosed fuse cut-outs classified as 
required under No. 52 q. Again, the voltag-e in most plants 
can, under some conditions, rise considerably above the nor- 
mal. The need of some margin, as a factor of safety to pre- 
vent the cut-outs from being" ruined in ordinary service, is 
therefore evident. 

The most severe service which can be required of a cut-out 
in practice is to open a "dead short-circuit" with only one 
fuse blowing, and it is with these conditions that all tests 
should be made. (See Section j.) 

d. Circuit-breakers must operate successfully on short-cir- 
cuits, under the most severe conditions with which they are 
liable to meet in practice, at 25 per cent above their rated 
voltage and with the circuit-breaker set at the highest pos- - 
sible opening point. \ 

For the sarwe reason as in Section c. 

e. Must be plainly marked where it will always be visible, 
with the name of the maker, and current and voltage for which 
the devpce is designed. 

Link-Fuse Cut-Outs. 

{See Figure 159.) 
(Cut-outs of porcelain are not approved for link fuses.) 
The following rules are intended to cover open link fuses 
m.ounted on slate or marble bases, including switchboards, 
tablet-boards, and single fuse-blocks. They do not apply to 
fuses mounted on porcelain bases, to the ordinary porcelain 
cut-out blocks, enclosed fuses, or any special or covered type 
of fuse. When tablet-boards or single fuse-blocks with such 
open link fuses on them are used in general wiring, they must 
be enclosed in cabinet boxes made to meet the requirements of 
No. 54. This is necessary, because a severe flash may occur 
when such fuses melt, so that they would be dangerous if 
exposed in the neighborhood of any combustible material. 

f. Base. — Must be mounted on slate or marble bases. 
Bases with an area of over twenty-five square inches must 
have at least four supporting screws. Holes for supporting 
screws must be kept outside of the area included by the out- 
side edges of the fuse-block terminals and must be so located 
or countersunk that there will be at least one-half an inch 
space, measured over the surface, between the head of the 
screw or washer and the nearest live part. 

. g. Mounting. — Nuts or screw-heads on the under side 



2GG 



MODERN ELECTRICAL CONSTRUCTION. 



of the base must be countersunk not less than one-eighth inch, 
and covered with a waterproof compound which will not melt 
below 150 degrees Fahrenheit, 





Figure 159 



Figure 160. 



h. Metal. — All fuse-block terminals must have ample 
metal for stiffness and to prevent rise in temperature of any 
part of over 50 degrees Fahrenheit at full load. Terminals, as 
far as practicable, should be made of compact form instead of 
being rolled out in thin strips ; and sharp edges or thin pro- 
jecting pieces as on winged thumb nuts and the like should be 
avoided. Thin metal, sharp edges and projecting pieces are 
much more likely to cause an arc to start than a more solid 
mass of metal. It is a good plan to round all corners of the 
terminals and to chamfer the edges. 

7. Connections. — Clamps for connecting the wires to 
the fuse-block terminals must be of solid, rugged construction, 
so as to insure a thoroughly good connection and to withstand 
considerable hard usage. For fuses rated at over thirty 
amperes tugs firmly screwed or bolted to the terminals and 
into which the conducting wires are soldered must be used. 

See note under No. 51 h. 

y. Test. — Must operate successfully when blowing only 
one fuse at a time on short-circuits with fuses rated at 50 
per cent above and with a voltage 25 per cent above the 
current and voltage for which the cut-out is designed. 

k. Marking. — Must be plainly marked, where it will be 



FITTINGS, MATERIALS, ETC. 207 

visible when the cut-off block is installed, with the name of 
the maker and the current and the voltage for which the 
block is designed. 

/. Spacings. — Spacings must be at least as great as 
those given in the following table, which applies only to plain, 
open link-fuses mounted on slate or marble bases. The spac- 
ings given are correct for fuse-blocks to be used on direct- 
current systems, and can therefore be safely followed in devices 
designed for alternating currents. If the copper fuse-tips over- 
hang the edges of the fuse-block terminals, the spacings should 
be measured between the nearest edges of the tips. 

Minimum Separation of Minimum 

Nearest Metal Parts of Break- 

125 volts or less: Opposite Polarity. Distance. 

10 amperes or less % inch. % inch. 

11-100 amperes 1 " % " 

101-103 •' 1 " 1 

301-1000 " 11/4 '• 1% *' 

126 to 250 volts: 

10 amperes or less iy2 inch. 1 ^4 inch. 

11-100 amperes 1 % '• 1 14 " 

101-300 '♦ 2 " iy2 " 

301-1000 " 21/2 " 2 

A space must be maintained between fuse terminals of the 
same polarity of at least one-half inch for voltag-es up to 125 
and of at least three-quarter inch for voltages from 126 to 250. 
This is the minimum distance allowable, and greater separa- 
tion should be provided when practicable. 

For 250 volt boards or blocks with the ordinary front-con- 
nected terminals, except where these have a mass of compact 
form, equivalent to the back-connected terminals usually found 
in switchboard work, a substantial barrier of insulating ma- 
terial, not less than one-eighth of an inch in thickness, must 
be placed in the "break-gap" — this barrier to extend out from 
the base at least one-eighth of an inch farther than any bare 
live part of the fuse-block terminal, including binding screws, 
nuts and the like. (Figure 160.) 

For three-wire systems cut-outs must have the break-dis- 
tance reo.uired for circuits of the potential of the outside 
wires. 

Enclosed-Fuse Cut-Outs — Plug and Cartridge Type. 

(See Figure 161.) 

m. Base. — Must be made of non-combustible, non- 
absorptive insulating material. Blocks with an area of over 



2G8 MODEliN ELECTIUCAL CONSTRUCTION. 

twenty-five square inches must have at least four supporting 
screws. Holes for supporting screws must be so located or 
countersunk that there will be at least one-half of an inch 
space, measured over the surface, between the screw-head or 
washer and the nearest live metal part, and in all cases when 
between parts of opposite polarity must be countersunk. 

77. Mountings. — Nuts or screw-heads on the under side 
of the base must be countersunk at least one-eighth of an inch 
and covered with a waterproof compound which will not melt 
below 150 degrees Fahrenheit. 

o. Terminals. — Terminals must be of either the Edi- 
son plug, spring clip or knife blade type, of approved design, 
to take the corresponding standard enclosed fuses. They 
must be secured to the base by two screws or the equivalent, 
so as to prevent them from turning, and must be so made as 
to secure a thoroughly good contact with the fuse. End stops 





Figure 161. 

must be provided to insure the proper location of the cartridge 
fuse in the cut-out. 

p. Connections. — Clamps for connecting wires to the 
terminals must be of a design which will insure a thoroughly 
good connection, and must be sufficiently strong and heavy to 
withstand considerable hard usage. For fuses rated to carry 
over thirty amperes, lugs firmly screwed or bolted to the 
terminals and into which the connecting wires shall be soldered 

nrist be used. 

« 

q. Classification. — Must be classified as regards both 
current and voltage as given in the following table, and must 
he so designed that the bases of one class cannot be used 
with fuses of another class rated for a higher current or 
voltage. 



0-250 Volts. 


0- 


• 30 amperes. 


31- 


■ 60 


61- 


■100 


101- 


■200 


201- 


■400 


401- 


■600 



fittings, materials, etc. 269 

251-600 Volts. 
0- 30 amperes. 

31- 60 

61-100 
101-200 
201-400 

r. Design. — Must be of such a design that it will not 
be easy to form accidental short-circuits across live metal parts 
of opposite polarity on the block or on the fuses in the block. 

.9. Marking. — Must be marked, where it will be plainly 
visible when the block is installed, with the name of the maker 
and the voltage and range of current for which it is designed. 

53. Fuses. 

(For installation rules, see Nos. ly and 21.) 

Link Fuses. 

a. Terminals. — Must have contact surfaces or tips of 
harder metal, having perfect electrical connections with the 
fusible part of the strip. 

The use of the hard metal tip is to afford a strong mechani- 
cal bearing for the screws, clamps, or other devices provided 
for holding the fuse. 

b. Rating. — ^lust be stamped with about 80 per cent of 

the maximum current which they can carry indefinitely, thus 

allowing about 25 per cent overload before the fuse melts. 

With naked open fuses, of ordinarj^ shapes and witli not 
over 500 amperes capacity, the minimum current which will 
melt them in about five minutes may be safely taken as the 
melting" point, as the fuse practically reaches its maximum 
temperature in this time. With larger fuses a longer time is 
necessary. This data are given to facilitate testing. 

c. Marking. — Fuse terminals must be stamped with 
the maker's name or. initials, or with some known trade mark. 

Enclosed Fuses — Plug and Cartridge Type. 

(See Figure 161.) 

These requirements do not apply to fuses for rosettes, at- 
taehmenf plugs, car lighting, cut-outs and protective devices 
for signaling systems. 



270 MODERN ELECTRICAL CONSTRUCTION. 

d. Construction. — The fuse plug or cartridge must be 
sufficiently dust-tight so that lint and dust cannot collect 
around the fusible wire and become ignited when the fuse is 
blown. 

The fusible wire must be attached to the plug or cartridge 
terminals in such a way as to secure a thoroughly good con- 
nection and to make it difficult for it to be replaced when 
melted. 

e. Classification. — Must be classified to correspond 
with the different classes of cut-out blocks, and must be so 
designed that it will be impossible to put any fuse of a given 
class into a cut-out block which is designed for a current or 
voltage lower than that of the class to which the fuse belongs. 

/. Terminals. — The fuse terminals must be sufficiently 
heavy to ensure mechanical strength and rigidity. 

The styles of terminals must be as follows : 

0-250 Volts. 

iC a, spring clip 
J Cartridge fuse / to •< i^™!"^!^. 
Ai ,. 1 ^ ^N ," Ll ) ?), Edison 

I (ferrule contact) \ fit ( pi^g casings. 
B Approved plugs for Edison cut-outs. 

C a, spring clip * 

o. ar^ .. J Cartridge fuse ( to •< 7 terminals. 
31-60 •• < ,„ 1 ^ .X h L? ) ?<, Edison plug 

j (ferrule contact) ( fit (^ casings. 

61-100 '' ^ 

201-400 " r Cartridge fuse (knife blade contact). 
400-600 " ) 

251-600 Volts. ' 

31-60 '* [cartridge fuse (ferrule contact). 

61-100 " ) 
101-200 " VCartridge*f use (knife contact). 
201-400 •' ) 

g. Dimensions. — Cartridge enclosed fuses and corre- 
sponding cut-out blocks must conform to the dimensions given 
in the table attached. 



FITTINGS, MATERIALS, ETC. 271 

h. Rating. — Fuses must be so constructed that with 
the surrounding atmosphere at a temperature of 75 degrees 
Fahrenheit (24 degrees Centigrade) they will carry indefinitely 
a current 10 per cent greater than that at which they are rated 
and at a current 25 per cent greater than the rating they will 
open the circuit without reaching a temperature which will in- 
jure the fuse tube or terminals of the fuse block. With a cur- 
rent 50 per cent greater than the rating and at room tempera- 
ture of 75 degrees > Fahrenheit (24 degrees Centigrade), the 
fuses starting cold, must blow within the time specified below : 
0- 30 amperes, 30 seconds. 

31- 60 " 1 minute. 

61-100 " 2 minutes. 

101-200 " 4 

201-400 " 8 

401-600 " 10 

i. Marking. — Must be marked, where it will be plainly 
visible, with the name or trade-mark of the maker, the volt- 
age ^nd current for which the fuse is designed, and the words 
"National Electrical Code Standard." Each fuse must have 
a labf^l, the color of which must be green for 250-volt fuses 
and red for 600-volt fuses. 

It will be satisfactory to abbreviate the above designation 
to "N. E. Code St'd" wliere space is necessarily limited. 

y. Temperature Rise. — The temperature of the ex- 
terior of the fuse enclosure must not rise more than 125 
degrees Fahrenheit (70 degrees Centigrade) above that of 
the surrounding air when the fuse is carrying the current for 
which it is rated. 

k. Test. — Must not hold an arc or throw out melted 
metal or sufficient flame to ignite easily inflammable material 
on or near the cut-out when only one fuse is blown at a time 
on a short circuit on a system of the voltage for which the 
fuse is rated. 

The normal capacity of the system must be in excess of 
the load on it just previous to the test by at least five times 
the rated capacity of the fuse under test. 

The resistimce of the circuit up to the cut-out terminals 
must be such that the impressed voltage at the terminals will 
be decreased not more than 1 per cent when a current of 
lOO amperes is passed between them. 



272 



MODERN ELECTRICAL CONSTRUCTION. 




TABLE OF DIMENSIONS OF THE 
STANDARD CARTRIDGE 



«-C-i|, 




STYLE OF TETRMINAU FQRCARTRlDGE: FUSES 
* 0-60 AMPERtS 



Form 1. CARTRIDGE FUSE— Ferrule Contact. 





Rated 
Capacity. 

Amperes. 


A 


B 


C 


Voltage. 


Length 

over 

Terminals. 

Inches. 


Distance 

between 

Contact 

Clips 

Inches. 


Width 

of 

Contact 

Clips. 

Inches, 


0-250 


0-30 
31-60 


B 2 
^ 3 


1 


H 

% 




61-100 
101-200 
201-400 
401-600 


° 8% 
^ 10% 




4 
6 


1% 
2H 


251-600 


0-30 
31-60 


E 5 
£ 5^ 


4 


% 




61-100 
101-200 
201-400 


^ 7% 

l2 11^8 


6 

7 
8 


% 
1'4 



FITTINGS, MATERIALS, ETC. 



273 



NATIONAL ELECTRICAL CODE 
ENCLOSED FUSE 



Jr-^- 



---J-- 

G 




STYLE or TERMINAL FOR CARTRi 
ffl-BOOAMPElRCS 



DGE FUSEsi 



Form 2. CARTRIDGE FUSE— Knife Blade Contact. 



D 


E 


F 


G 




Diameter of 

Ferrules or 

Thickness 

of Terminal 

Blades. 

Inches. 


Min. Length of 

Ferrules or of 

Terminal Blades 

outside of 

Tube. 

Inches. 


Dia. 

of 
Tube. 

Inches. 


' Width 

of 

Terminal 

Blades. 

Inches. 


Rated 
Capacity 

Amperes. 


1% 






3 


0-30 
31-60 




1 

1% 
2H 


1 

2 

2% 


IH 1 
2 -^ 


61-100 
101-200 
201-400 
401-600 


1^ 


% 


i-" 


3 


0-30 
31-60 


ft 


1 
1% 

178 


1^ 

2% 


IH i 

1% ro 


61-100 
101-200 
201-400 



274 



MODERN ELECTRICAL CONSTRUCTION, 



For convenience a current of different value may be used, 
in which case the per cent drop in voltage allowable would 
vary in direct proportion to the difference in current used. 

The above requirement regarding the capacity of the test- 
ing- circuit is to guard against making the test on a system 




Three- Wire Mains 

Figure 162. 



of so small capacity that the conditions would be sufficiently 
favorable to allow really poor fuses to stand the test accept- 
ably. On the other hand, it must be remembered that if the 
test is made on a system of very large capacity, and especi- 
ally if there is but little resistance between the generators 
and fuse, the conditions may be more severe than are liable to 
be met with in practice outside of the large power stations, 
the result being that fuses entirely safe for general use may 
be rejected if such test is insisted upon. 

53A. Tablet and Panel Boards. 

(See Fif^tire 162.) 



FITTINGS, MATERIALS, ETC. 



275 



The following niinimiim distance between bare live metal 
parts (bus-bars, etc.) must be maintained : 

Between parts of opposite polarity Between parts of 

except at switches and link fuses. same polarity. 

When mounted on When held free At link 

the same surface. in the air. fuses. 

0-125 volts % inch. % inch. 1/2 inch. 

126-250 volts 114 inch. % inch. % inch. 

At switches or enclosed fuses, parts of the same polarity 
may be placed as close together as convenience in handling 
will allow. 

It should be noted that the above distances are the mini- 
mum allowable, and it is urged that greater distances be 
adopted wherever the conditions will permit. 

The spacings given in the first column apply to the branch 
conductors where enclosed fuses are used. Where link fuses 
or* knife switches are used, the spacings must be at least as 
great as those required by Nos. 51 and 52. 

The spacings given in the second column apply to the dis- 
tance between the raised main bars and between these bars and 
the branch bars over which they pass. 

The spacings given in the third column are intended to 
prevent the meltingi of a link fuse by the blowing of an ad- 
jacent fuse of the same polarity. 



54. 



Cut-Out Cabinets. 

a. Material. — Cabinets must be 
substantially constructed of non-com- 
bustible, non-absorptive material, or of 
wood. When wood is used the inside 
of the cabinet must be completely lined 
with a non-combustible insulating ma- 
terial. Slate or marble at least one- 
quarter inch in thickness is strongly 
recommended for such lining, but, ex- 
cept with metal conduit systems, asbes- 
tos board at least one-eighth inch in 
thickness may be used in dry places if 
firmly secured by shellac and tacks. 

With metal conduit systems the lin- 
ing of either the box or the gutter must 
be one-sixteenth inch galvanized, painted 
or enameled steel, or, preferably, one- 
quarter inch slate or marble. (Figure 
163.) 




Fig. 163. 



276 MODERN ELECTRICAL CONSTRUCTION. 

The object of the lining- of such cut-out cabinets or gutters 
is to render the same approximately fireproof in case of short 
circuit after the wires leave the protecting metal conduits. 

Two thicknesses of 1-32 inch steel may be used instead 
of one of 1-16 inch. 

With wood cabinets the wood should be thoroughly filled 
and painted before the lining is put in place. 

b. Door. — The door must close against a rabbet, so 
as to be perfectly dust-tight. Strong hinges and a strong 
hook or catch are required. Glass doors must be glazed 
with heavy glass, not less than ^ inch in thickness, and 
panes should not exceed 300 square inches in area. A space 
of at least two inches must be allowed between the fuses and 
the door. This is necessary to prevent cracking or breaking 
by the severe blow and intense heat which may be produced 
under some conditions. 

A cabinet is of little use unless the door is kept tightly 
closed, and especial attention is therefore called to the im- 
portance of having a strong and reliable catch or other fast- 
ening. A spring catch is advised if a good one can be ob- 
tained, but most of those sold for use on cupboards, etc., are 
so small that they fail to catch when the door shrinks a little, 
or are so weak that they soon give out. 

It is advised that the bottoms of cabinets be given a de- 
cided slant to prevent their use as a shelf, as well as the 
accumulation of dust, etc. 

c. Bushings. — Bushings through which wires enter 
must fit tightly the holes in the box, and must be of approved 
construction. The wires should completely fill the holes in the 
bushings, using tape to build up the wire, if necessary, so as 
to keep out the dust. 

Rule 54A. Rosettes. 

(See Figure 164.) 

Ceiling rosettes, both fused and fuseless, must be con- 
structed in accordance with the following specifications: 

a. Base. — Current-carrying parts must be mounted on 
non-combustible, non^absorptive insulating bases. There 
should be no openings through the rosette base except those 
for the supporting screws and in the concealed type for the 
conductors also, and these openings should not be made any 
larger than necessary. 

There must be at least one-quarter inch space, measured 



FITTINGS, MATEllIALS, ETC. 



277 



over the surface, between supporting screws and current- 
carrjang parts. The supporting screws must be so located 
or countersunk that the flexible cord cannot come in contact 
with them. 

Bases for the knob and cleat type must have at least two 
holes for supporting screws ; must be high enough to keep the 
wires and terminals at least one-half inch from the surface 





Figure 164. 



to which the rosette is attached, and must have a porcelain 
lug under each terminal to prevent the rosette from being 
placed over projections which would reduce the separation to 
less thani one-half inch. 

Bases for the moulding and conduit box types must be high 
enough to keep the wires and terminals at least three-eighths 
inch from the surface wired over. 

b. Mounting. — Contact pieces and terminals must be 
secured in position by at least two screws, or made with a 
square shoulder, or otherw^ise arranged to prevent turning. 

The nuts or screw heads on the under side of the base must 
be countersunk not less than one-eighth inch and covered with 
a waterproof compound which will not melt below 150 degrees 
Fahrenheit. 

c. Terminals. — Line terminal plates must be at least 
.07 inch in thickness, and terminal screws must not be smaller 
than No. 6 standard screw\s with about 32 threads per inch. 

Terminal plates for the flexible cord and for fuses must 
be at least .06 inch in thickness. The connection to these 
plates shall be by binding screws not smaller than No. 5 



278 MODEEN ELECTKICAL CONSTRUCTION. 

Standard screw with about 40 threads per inch. At all 
binding screws for line wires and for flexible cord, up-turned 
lugs, or some equivalent arrangement, must be provided which 
will secure the wires being held under the screw heads. 

d. Cord Inlet. — The diameter of the cord inlet hole 
should measure 13/32 inch in order that standard portable 
cord may be used. 

c. Knot Space. — Ample space must be provided for a 
substantial knot tied in the cord as a whole. 

All parts of the rosette upon which the knot is likely to 
bear must be smoolh and well rounded. 

/. Cover. — When the rosette is made in two parts the 
cover must be secured to the base so that it will not work 
loose. 

In fused rosettes, the cover must lit closely over the base 
so as to prevent the accumulation of dust or dirt on the 
inside, and also to prevent any flash or melted metal from 
being thrown out w^hen the fuses melt. 

g. Markings. — Must be plainly marked where it may 
readily be seen after the rosette has been installed, with the 
iiame or trade mark of the manufacturer, and the rating in 
amperes and volts. Fuseless rosettes may be rated 3 amperes, 
250 volts ; fused rosettes, with link fuses, not over 2 amperes, 
125 volts. 

h. Test. — Fused rosettes must have a fuse in each pole 
and must operate successfully when short-circuited on the volt- 
age for which they are designed, the test being made with 
the two fuses in circuit. 

NOTE. — When link fuses are used the test shall be made 
with fuse wire which melts at about 7 amperes in one inch 
lengths. The larger fuse is specified for the test in order to 
more nearly approximate the severe conditions obtained when 
only one 2-ampere fuse (the rating" of the rosette) is blown 
at a time. 

Fused rosettes equipped with enclosed fuses are much 
preferable to the link fuse rosettes. 

55. Sockets. 

(See Figure 165.) 
(For installation rules, see No. 27.) 



FITTINGS, MATERIALS, ETC. 



279 



Sockets of all kinds, including- wall receptacles, must be 
constructed in accordance with the following specifications: 

a. Standard Sizes. — The standard lamp socket must be 
suitable for use on any voltage not exceeding 250 and with 
any size lamp up to 50 candle-power. For lamps larger than 
50 candle-power a standard keyless socket may be used, or 
if a key is required a special socket designed for the current 
to be used must be made. Any special sockets must follow the 
general spirit of these specifications. 

b. Marking. — All sockets must be marked with the 
manufacturer's name or trade-mark. ^The standard key 
socl^et must also be plainly marked 250 v. 50 c. p. Receptacles, 
keyless sockets and special sockets must be marked with the 
current and voltage for which they are designed. 

c. Shell. — Metal used for shells must be moderately 
hard, but not hard enough to be brittle or so soft as to be 




Figure 165. 

easily dented or knocked out of shape. Brass shells must be 
at least thirteen one-thousandths of an inch in thickness, and 
shells of any other material must be thick enough to give the 
same stiffness and strength as the required thickness of brass. 
d. Lining. — The inside of the shells must be lined with 
insulating material, which must absolutely prevent the shell 
from becoming a part of the circuit, even though the wires 
inside the socket should start from their position under the 
binding screws. 

The material used for lining must be at least one thirty- 
second of an inch in thickness and must be tough and 
tenacious. It must not be injuriously affected by the heat 
from the largest lamp permitted in the socket, and must leave 



280 modp:kn electrical construction. 

water in which it is boiled practically neutral. It must be so 
tirmly secured to the shell that it will not fall out with 
ordinary handling of the socket. It is preferable to have the 
lining in one piece. 

The cap must also be lined, and this lining must comply 
with the requirements for shell linings. 

The shell lining- should extend beyond the shell far enough 
so that no part of the lamp base is exposed when a lamp is in 
the socket. 

The standard Edison lamp base measures ^| inch, in a 
vertical plane from the bottom of the center contact to the 
upper edge of the screw shell. 

In sockets and receptacles of standard forms a ring of 
any material inserted between an outer metal shell of the 
device and the inner screw shell for insulating purposes and 
separable from the device as a whole is considered an un- 
desirable form of construction. This does not apply to the 
use of rings in lamp clusters or in devices where the outer 
shell is of porcelain, where such rings serve to hold the 
several porcelain parts together, and are thus a necessary 
part of the whole structure of the device. 

e. Cap. — Caps, when of sheet brass, must be at least 
thirteen one-thousandths of an inch in thickness, and when 
cast or made of other metals must be of equivalent strength. 
The inlet piece, except for special sockets, must be tapped 
with a standard one-eighth-inch pipe thread. It must contain 
sufficient metal for a full, strong thread, and when not in one 
piece with the cap must be joined to it in such a way as to 
give the strength of a single piece. 

There must be sufficient room in the cap to enable the 
ordinary wireman to easily and quickly make a knot in the 
cord and to push it into place in the cap without crowding. 
All parts of the cap upon which the knot is likely to bear must 
be smooth and well insulated. 

The cap lining called for in the note to Section rl V7\\\ pro- 
vide a sufficiently smooth and well-insulated surface for the 
knot to bear upon. 

Sockets with an outlet threaded for three-eighths inch 
pipe will, of course, be approved where circumstances demand 
their use. This size outlet is necessary with most stiff 
pendants and for the proper use of reinforced flexible cord, as 
explained in the note to No. 28 (J. 

f. Frame and Screws. — The frame which holds the 



FITTINGS^ MATEKIALS^ ETC. 281 

moving parts must be sufficiently heavy to give ample strength 
and stiffness. 

Brass pieces containing screw threads must be at least 
six one-hundredths of an inch in thickness. 

Binding post screws must not be smaller than No. 5 stand- 
ard screw with about 40 threads per inch. 

g. Spacing. — Points of opposite polarity must every- 
where be kept not less than three sixty-fourths of an inch 
apart, unless separated by a reliable insulation. 

h. Connections. — The connecting points for the flex- 
ible cord must be made to very securely grip a No. 16 or 18 
B. & S. gage conductor. A turned-up lug, arranged so that 
the cord may be gripped between the screw and the lug in such 
a way that it cannot possibly come out, is strongly advised. 

/. Lamp Holder. — The socket must firmly hold the 
lamp in place so that it cannot be easily jarred out, and must 
provide a contact good enough to prevent undue heating with 
the maximum current allowxd. The holding pieces, springs, 
and the like, if a part of the circuit, must not be sufficiently 
exposed to allow them to be brought in contact with anything 
outside of the lamp and socket. 

/. Base. — With the exception of the lining all parts of 
insulating material inside the shell must be made of por- 
celain. 

k» Key. — The socket key-handle must be of such a 
material that it will not soften from the heat of a fifty candle- 
power lamp hanging downwards from the socket in air at 70 
degrees Fahrenheit, and must be securely, but not necessarily 
rigidly, attached to the metal spindle which it is designed to 
turn. 

/. Sealing. — All screws in porcelain pieces, which can 
be firmly sealed in place, must be so sealed by a waterproof 
compound which will not melt below 200 degrees Fahrenheit. 

;;/. Putting Together. — The socket as a whole must be 
so put together that it will not rattle to pieces. Bayonet 
joints or an equivalent are recommended. 

11. Test. — The socket, wdien slowly turned "on and 
off" at the rate of about two or three times per minute, 



282 MODERN ELECTRICAL CONSTRUCTION. 

while carrying a load of one ampere at 250 volts, must "make 
and break" the circuit 6,000 times before failing. 

0. Keyless Sockets. — Keyless sockets of all kinds 
must comply with the requirements for key sockets as far as 
they apply. 

p. Sockets of Insulating Material. — Sockets made of 
porcelain or other insulating material must conform to the 
above requirements as far as they apply, and all parts must 
be strong enough to withstand a moderate amount of hard 
usage without breaking. 

Porcelain shell sockets being- subject to breakage, and con- 
stituting- a hazard when broken, will not be accepted for use 
in places where they would be exposed to hard usage. 

q. Inlet Bushing. — When the socket is not attached 
to a fixture, the threaded inlet must be provided w^ith a strong 
insulating bushing having a smooth hole at least nine thirty- 
seconds of an inch in diameter. The edges of the bushing 
must be rounded and all inside fins removed, so that in no 
place will the cord be subjected to the cutting or wearing 
action of a sharp edge. 

Bushings for sockets having- an outlet threaded for three- 
eighths-inch pipe should have a hole thirteen thirty-seconds of 
an inch in diameter, so that they will accommodate approved 
reinforced flexible cord. 

56. Hanger-Boards. 

(See Figure i66.) 

a. Hanger-boards must be so constructed that all wires 
ind current-carrying devices thereon will be exposed to view 





Figure 166. 

and thoroughly insulated by being mounted on a non-com- 
bustible, non-absorptive insulating substance. All switches 



FITTINGS^ MATERIALS, ETC. 



283 



attached to the same must be so constructed that they shall 
be automatic in their action, cutting off both poles to the lamp, 
not stopping between points when started and preventing an 
arc between points under all circumstances. 

57. Arc Lamps. 

(See Figure 167.) 
(For installation rules, see Nos. ig and 2g.) 

a. Must be provided witlT reliable stops to prevent car- 
bons from falling out in case the lamps become loose. 

b. All exposed parts must be carefully insulated from the 
circuit. 

c. Must, for constant-current systems, be provided with 
an approved hand switch, and an automatic switch that will 

shunt the current around the carbons, 
should they fail to feed properly. 

The hand switch to be approved, if 
placed anywhere except on the lamp 
itself, must comply with requirements 
for switches on hanger-boards as laid 
down in No. 56. 




Figure 167 



58. Spark Arresters. 

(See Figure 167.) 

(For installation rules, see Nos. 19 c 

and 29 c.) 

a. Spark arresters must so close 
the upper orifice of the globe that it 
will be impossible for any sparks, 
thrown out by the carbons, to escape. 
59. Insulating Joints. 

(See No. 26 a.) 

a. Must be entirely made of material that will resist the 
action of illuminating gases, and will not give way or soften 
under the heat of an ordinary gas flame or leak under a mod- 
erate pressure. Must be so arranged that a deposit of mois- 
ture will not destroy the insulating effect; must show a 



284 MODERN ELECTRICAL CONSTRUCTION. 

dielectric Strength between gas-pipe attachments sufficient to 
resist throughout five minutes the application of an electro- 
motive force of 4,000 volts ; and must be sufficiently strong to 
resist the strain to which they are Hable to be subjected 
during installation. 

/7. Insulating joints having soft rubber ni their construc- 
tion will not be approved. 

60. Rheostats. 

(For installation rules, see Nos. 4 a and 8 c.) 

a. Materials. — Must be made entirely of non-com- 
bustible materials, except such minor parts as handles, magnet 
insulation, etc. 

All segments, lever arms, etc., must be mounted on non- 
combustible, non-absorptive insulating material. 

Rheostats used in dusty or linty places or where exposed 
to flying-s of combustible material must be so constructed 
that even if the resistive conductor be fused by excessive 
current the arc or any attendant flame will be quickly and 
safelv extinguished. Rheostats used in places where the 
above conditions do not exist may be of any approved type. 

b. Construction. — ^lust be so constructed that when 
mounted on a plane surface the casing will make contact with 
such surface only at the points of support. An air space of 
at least % inch between the rheostat casing and the support- 
ing surface will be required. 

The construction throughout must be heavy, rugged and 
thoroughly workmanlike. 

c. Connections. — Clamps for connecting wires to the 
terminals must be of a design which will ensure a thoroughly 
good connection, and must be sufficiently strong and heavy to 
withstand considerable hard usage. For currents above fifty 
amperes, lugs firmly screwed or bolted to the terminals, and 
into which the connecting wires shall be soldered, must be 
used. 

Clamps or lugs will not be required where leads designed 
for soldered connections are provided. 

d. Marking.^— ]\Tust be plainly marked, where it may 
be readily seen after the device is installed, with the rating and 
the name of the maker ; and the terminals of motor-starting 



FITTINGS, MATEKIALS, ETC. 285 

rheostats must be marked to indicate to what part of the 
circuit each is to be connected, as "Hne," "armature," and 
"field." 

e. Contacts. — The design of the fixed and movable 
contacts and the resistance in each section must be such as to 
secure the least tendency toward arcing and roughening of the 
contacts, even with careless handling or the presence of dirt. 

In motor-starting rheostats, the contact at which the cir- 
cuit is broken by the lever arm when moving from the running 
to the starting position must be so designed that there will 
be no detrimental arcing. The final contact, if any, on which 
the arm is brought to rest in the starting position must have 
no electrical connection. 

Experience has shown that sharp edges and segments of 
thin material help to maintain an arc, and it is recommended 
that these be avoided. Segments of heavy construction have 
a considerable cooling- effect on the arc, and rounded corners 
tend to spread it out and thus dissipate it. 

It is recommended that the circuit-breaking contacts be 
so constructed as to "break" with a quick snap, independently 
of the slowness of movement of the operator's hand, or that 
a magnetic blowout or equivalent device be used. For dial 
type rheostats the movable contact should be flexible in a 
plane at right angles to the plane of its movement, and f'or 
medium and larger sizes the stationary contacts should be 
readily renewable. 

f. No-voltage release. — Motor-starting rheostats must 
be so designed that the contact arm cannot be left on inter- 
mediate segments, and must be provided with an automatic 
device which will interrupt the supply circuit before the speed 
of the motor falls to less than one-third of its normal value. 

g. Overload-release. — Overload-release devices which 
are inoperative during the process of starting a motor will 
not be approved, unless other circuit-breakers or fuses are 
installed in connection with them. 

If, for instance, the overload-release device simply releases 
the starting arm and allows it to fly back and break the circuit, 
it is inoperative while the arm is being moved from the start- 
ing to the running position. 

h. Test. — Must, after 100 operations under the most 
severe normal conditions for which the device is designed, 
show no serious burning of the contacts or other faults, and 



286 MODERN ELECTRICAL CONSTKUCTIOX. 

the release mechanism of motor-starting rheostats must not 
be impaired by such a test. 

Field rheostats, or main-line regulators intended for con- 
tinuous use, must not be burned out or depreciated by carry- 
ing the full normal current on any step for an indefinite period. 
Regulators intended for intermittent use (such as on electric 
cranes, elevators, etc.) nmst be able to carry their rated cur- 
rent on any step for as long a time as the character of the 
apparatus which they control will permit them to be used 
continuously. 

61. Reactive Coils and Condensers. 

a. Reactive coils must be made of non-combustible ma- 
terial, mounted on non-combustible bases and treated, in 
general, as sources of heat. 

b. Condensers must be treated like other apparatus oper- 
ating with equivalent voltage and currents. They must have 
non-combustible cases and supports, and must be isolated 
from all combustible materials and, in general, treated as 
sources of heat. 

62. Transformers. 

{For installation rules, see Mas. ii, 13, 13A and 36.) 

a. Must not be placed in any but metallic or other non- 
combustible cases. 

On account of the possible dangers from burn-outs in the 
coils. (See note under No. 11 a.) 

It is advised that every transformer be so designed and 
connected that the middle point of the secondary coil can 
be reached if, at any future time, it should be desired to 
ground it. 

h. Must be constructed to comply with the following 
tests : 

1. Shall be run, for eight consecutive hours at full load 
in watts under conditions of service, and at the 
end of that time the rise in temperature, as meas- 
ured by the increase of resistance of the primary 
coil, shall not exceed 175 degrees Fahrenheit 
(97 degrees Centigrade). 



FITTINGS. MATERIALS, ETC. 287 

2. The insulation of transformers when heated shall 
withstand continuously for five minutes a differ- 
ence of potential of 10,000 volts (alternating) be- 
tween the primary and secondary coils and be- 
tween the primary coils and core, and a no-load 
"run" at double voltage for thirty minutes. 

63. Lightning Arresters. 

(For installation rules, see No. 5.) 

a. Lightning arresters mus.t be of approved construc- 
tion. (See list of Electrical Fittings.) 



Class E. 

MISCELLANEOUS. 

64. Signaling Systems. 

Governing zviring for telephone, telegraphy district mes- 
senger and eall-hell circuits, tire and burglar alarms, and all 
similar systems which are hazardous only because of their 
liability to become crossed urith electric light, heat or power 
circuits, 

a. Outside wires should be run in underground ducts or 
strung on poles, and, kept off of the roofs of buildings, ex- 
cept by special permission of the Inspection Department hav- 
ing jurisdiction, and must not be placed on the same cross- 
arm with electric light or power wires. They should not oc- 
cupy the same duct, manhole or handhole of conduit systems 
with electric light or power wires. 

Sing-le manholes, or handholes, may be separated in sec- 
tions by means of partitions of brick or tile so as to be con- 
sidered as conforming" with the above rule. 

The liability of accidental crossing- of overhead signaling 
circuits with electric lig-ht and power circuits may be guarded 
ag:ainst to a considerable extent by endeavoring- to keep the 
two classes of circuits on different sides of the same street. 

When the entire circuit from Central Station to "building" is 
run in underground conduits, Sections h to m 
inclusive do not apply. 

h. When outside wires are run on same pole with electric 
light or power wires, the distance between the two inside pins 
Oi each cross-arm must not be less than twenty-six inches. 

Sig-naling- wires being- smaller and more liable to break and 
fall, should generally be placed on the lower cross-arms. 

r. Where the wires are attached to the outside walls of 
buildings they must have an approved rubber insulating cov- 
ering (see No. 41), and on frame buildings or frame portions 
of other buildings shall be supported on glass or porcelain in- 
sulators, or knobs. 

d. The wires from last outside support to the cut-outs or 



MISCELLANEOUS. 289 

protectors must be of copper, and must have an approved 
rubber insulation (see No. 41) ; must be provided with drip 
loops immediately outside the buildings and at entrance ; 
mus.t be kept not less than two and one-half inches apart, ex- 
cept when brought in through approved metal-covered cables. 

e. Wires must enter building through approved non-com- 
bustible, non-absorptive insulating bushings sloping upward 
from the outside. 

Installations where the Current Carrying Parts of the Ap 
paratus Installed are Capable of Carrying Indefinitely c 
Current of Ten Amperes. 

f. An all-metallic circuit shall be provided, except in 
telegraph systems. 

g. At the entrance of wires to buildings, approved single 
pole cut-outs, designed for 251-600 volts potential and con- 
taining fuses rated at not over ten amperes capacity, shall be 
provided for each wire. These cut-outs must not be placed 
in the immediate vicinity of easily ignitible stuff, or where 
exposed to inflammable gases, or dust or to flyings of com- 
bustible material. 

h. The wires inside building shall be of copper not less 
than No. 16 B. & S. gage, and must have insulation 
and be supported, the same as would be required for an in- 
stallation of electric light or power wiring, 0-600 volts poten- 
tial. 

i. The instruments shall be mounted on bases con- 
s.tructed of non-combustible, non-absorptive insulating ma- 
terial. Holes for the supporting screws must be so located, 
or countersunk, that there will be at least one-half inch space, 
measured over the surface, between the head of the screw 
and the nearest live metal part. 

Installations where the Current Carrying Parts of the Ap- 
paratus Installed are Not Capable of Carrying Indefi- 
nitely a Current of Ten Amperes. 

j. Must be provided wnth an approved protective device 
located as near as possible to the entrance of wires to build- 
ing. The protector must not be placed in the immediate 



290 MODERN ELBCTRICAL CONSTRT'CTION. 

vicinity of easily ignitible stuff, or where exposed to inflam- 
mable gases, or dust or flyings of combustible material. 

k. Wires from entrance to building to protector must 
be supported on porcelain insulators, so that they will come 
in contact with nothing except their designed supports. 

/. The ground wire of the protective device shall be run 
in accordance with the following requirements: 

1. Shall be of copper and not smaller than No. 18 

B. & S. gage. 

2. Must have an approved insulating covering as de- 

scribed in No. 41, for voltages from .to 600, 
except that the preservative compound specified 
in No. 41, Section h, may be omitted. 

3. Must run in as straight a line as possible to a good 

permanent ground. This may be obtained by 
connecting to a water or gas pipe connected .to 
the street mains or to a ground rod or pipe 
driven in permanently damp earth. When con- 
nections are made to pipes, preference shall be 
given to water pipes. If attachment is made to 
gas pipe, the connection in all cases must be 
made between the meter and the street mains. 
In every case the connection shall be made as 
near as possible to the earth. 

When the ground wire is attached to water or gas 
pipes, these pipes shall be thoroughly cleaned 
and tinned with resin flux solder, if such a 
method is practicable ; the ground wire shall then 
be wrapped tightly around the pipe and 
thoroughly soldered to it. 

When the above method is impracticable, then if there 
are fittings where a brass plug can be inserted, 
the grourid wire shall be thoroughly soldered to 
it ; if there are no such fittings, th'en the pipe 
shall be thoroughly cleaned and an approved 
ground clamp fastened to an exposed portion 
of the pipe and the ground wire well soldered to 
the ground clamp. 



MISCELLANEOUS. 291 

When the ground wire is attached to a ground rod 
driven into the earth, the ground wire shall be 
soldered to the rod in a similar manner. 

Steam or hot-water pipes must not be used for a pro- 
tector ground. 

m. The protector to be approved must comply with the 
following requirements : 

For Instrument Circuits of Telegraph Systems. 

1. An approved single pole cut-out, in each wire, de- 
signed for 2,000 volts potential, and containing fuses 
rated at not over one ampere capacity. When main 
line cut-outs are installed as called for in section g, 
.the instrument cut-outs may be placed between the 
switchboard and the instrument as near the switch- 
board as possible. 

For All Other Systems. 

1. Must be mounted on non-combustible, non-absorptive 

insulating bases, so designed that when the pro.tector 
is in place all parts which may be alive will be 
thoroughly insulated from the wall to which the pro- 
tector is attached. 

2. Must have the following parts : 

A lightning arres.ter which will operate with a difference 
of potential between wires of not over 500 volts, and 
so arranged that the chance of accidental grounding 
is reduced to a minimum. 

A fuse designed to open the circuit in case the wires be- 
come crossed with light or power circuits. The fuse 
mu&t be able to open the circuit without arcing or 
serious flashing when crossed with any ordinary com- 
mercial light or power circuit. 

A heat coil, if the sensitiveness of the instrument de- 
mands it, which will operate before a sneak current 
can damage the instrument the protector is guard- 
ing. 

Heat coils are necessary in all circuits normally closed 
throug-h mag-net windings, wiiicli cannot indefinitely carry 
a current of at least five amperes. 

The heat coil is designed to warm up and melt out with a 



292 MODEKN ELBCTIJICAL CONSTRUCTION. 

current large enough to endanger the instruments if con- 
tinued for a long time, but so small that it would not 
blow the fuses ordinarily found necessary for such in- 
struments. The small currents are often called "sneak" 
currents. 

3. The fuses must be so placed as to protect the arrester 
and heat coils, and the protector terminals must be 
plainly marked "line," ''ins.trument," ''ground.'" 

An easily read abbreviation of the above words will be al- 
lowed. 

The Following* Bules Apply to All Systems whether the 

Wires from the Central Office to the Building* are 

Overhead or Underg'roimd. 

n. Wires beyond the protector, or wires inside buildings 
where no protector is used, must be neatly arranged and se- 
curely fastened in place in some convenient, workmanlike 
manner. They must not come nearer than six inches to any 
electric light or power wire in the building unless encased in 
approved tubing so secured as .to prevent its slipping out of 
place. 

The wires would ordinarily be insulated, but the kind of 
insulation is not specified, as the protector is relied upon to 
stop all dangerous currents. Porcelain tubing or approved 
flexible tubing may be used for encasing wires where required 
as above. 

0. Wires where bunched together in a vertical run within 
any building must have a fire-resisting covering sufficient to 
prevent the wires from carrying fire from floor to floor 
unless they are run either in non-combustible tubing or in a 
fireproof shaft, which shaft shall be provided with fire stops 
at each floor. 

Signaling wires and electric light or power wires may be 
run in the same shaft, provided that one of these classes 
of wires is run in non-combustible tubing, or provided that 
when run otherwise these two classes of wires shall be sep- 
arated from each o.ther by at least two inches. 

Tn no case shall ^signaling wires be run in the same tube 
with electric light or power wires. 

Ordinary rubber insulation is inflammable, and when a 
number of wires are contained in a shaft extending througn 
a building they afford! a ready means of carrying flre from 
floor to floor, unless they are covered with a fire-resisting 



MISCELLANEOUS. 293 

material, or unless the shaft is provided with flre stops at 
each floor. 

65, Electric Gas Lighting. 

a. Electric gas lighting must not be used on the same 

fixture with the electric light. 

The above rule does not apply to frictional systems of gas 
lighting. 

65 A. Moving Picture Machines. 

(/. Arc lamp used as a part of moving picture machines 
must be constructed similar to arc lamps of theaters and 
wiring of same must not be of less capacity than No. 6 B. 
& S. gage. (See No. 31A d. [1].) 

b. Rheostats must conform to rheostat requirements for 
theater arcs. (See No. 31A d [1].) 

c. Top reel must be encased in a steel box with hole at 
the bottom only large enough for film to pass through and 
cover so arranged that this hole can be instantly closed. No 
solder to be used in the construction of this box. 

d. A steel box must be used for receiving the film after 
being shown, with a hole in the top only large enough for 
the film to pas? through freely, with a cover so arranged that 
this hole can be instantly closed. An opening may be placed 
at the side of the box to take the film out, with a door hung 
at the top, so arranged that it cannot be entirely opened, and 
provided with spring catch to lock it closed. No solder to 
be used in the construction of this box. 

e. The handle or crank used in operating the machine 
must be secured to the spindle or shaft, so that there will 
be no liability of its coming off and allowing the film to stop 
in front of lamp. 

f. A shutter must be placed in front of the condenser, 
arranged so as to be readily closed. 

g. Extra films must be kept in metal box with tight fit- 
ting cover. 

h. Machines must be operated by hand (motor driven 
will not .be permitted). 

1. Picture machine must be placed in an enclosure or 
house made of suitable fireproof material, be thoroughly 



294 MODERN ELECTRICAL CONSTRUCTION. 

ventilated and large enough for operator to walk freely on 
either side of or back of machine. All openings into this 
booth must be arranged so as to be entirely closed by doors 
or shutters constructed of the same or equally good fire- 
resisting material as the booth itself. Doors or covers must 
be arranged so as to be held normally closed by spring 
hinges or equivalent devices. 

66. Insulation Resistance. 

The wiring in any building must test free from grounds; 
i. e., the complete installation must have an insulation be- 
tween conductors and between all conductors and the ground 
(not including attachments, sockets, receptacles, etc.), not 
less than that given in the following table : 

Up 



K.yj o ex 

10 


iiipci CO . 


2,000,000 


25 




800,000 


50 




400.000 


100 




200,000 


200 




100,000 


400 




50,000 


800 




25,000 


1,600 




12,500 



The test must be made with all cut-outs -and safety de- 
vices in place. If the lamp sockets, receptacles, electroliers, 
etc., are also connected, only one-half of the resistance speci- 
fied in the table will be required. 



CLASS R 

MARINE WORK. 

68. Generators. 

a. Must be located in a dry place. 

h. Must have their frames insulated from their bed- 
plates. 

c. Must each be provided with a w^aterproof cover. 

d. Must each be provided with a name-plate, giving the 
maker's name, the capacity in volts and amperes, and the 
normal speed in revolutions per minute. 

69. Wires. 

a. Must be supported in approved moulding or conduit, 
except at switchboards and for portables. 

Special permission may be given for deviation from this 
rule in dynamo-rooms. 

h. Mus.t have no single wire larger than No. 12 B. &: S. 
gage. Wires to be stranded when greater carrying capacity 
is required. No single solid wire smaller than No. 14 B. & 
S. gage, except in fixture wiring, to be used. 

Stranded wires must be soldered before being fastened 
under clamps or binding screws, and when they have a con- 
ductivity greater than that of No. 8 B. & S. gage copper wire 
they must be soldered into lugs. 

c. Splices or taps in conductors must be avoided as far 
as possible. Where it is necessary to make them they must 
be so spliced or joined as to be both mechanically and elec- 
trically secure without solder. They mus.t then be soldered, 
to insure preservation, covered with an insulating compound 
equal to the insulation of the wire, and further protected by 
a waterproof tape. The joist must then be coated or painted 
with a waterproof compound. 

All joints must be soldered unless made with some form of 
approved splicing device. 



29G MODERN ELECTIIICAL CONSTIiUCTION. 

For Moulding Work. 

d. Must have an approved insulating covering. 

The insulation for conductors, to be approved, must be at 
least 3-32 of an inch in thickness and be covered with a 
substantial waterproof braid. 

The physical characteristics sliall not be affected by any 
chang-e in temperature up to 200 deg-rees Fahrenheit (93 de- 
grees Centig"rade). After two weeks' submersion in salt water 
at 70 degrees Fahrenheit (21 degrees Centigrade), it must 
show an insulation resistance of 100 megohms per mile after 
three minutes' electrification with 550 volts. 

e. Must have, when passing through water-tight bulk- 
heads and through all decks, a metallic stuffing tube lined 
with hard rubber. In case of deck tubes, they must be boxed 
near deck to prevent mechanical injury. 

/. Must be bushed with hard rubber tubing, one-eighth 
of an inch in thickness, when passing through beams and 
non-water-tight bulkheads. 

For Conduit Work. 

g. Must have an approved insulating covering. 

The insulation for conductors, for use in lined conduits, 
to be approved, must be at least 3-32 of an inch in thickness 
and be covered with a substantial waterproof braid. The 
physical characteristics shall not be affected by any change 
in temperature up to 200 degrrees Fahrenheit (93 degrees 
Centigrade). 

After two weeks' submersion in salt water at 70 degrees 
Fahrenheit (21 degrees Centig-rade), it must show an insu- 
lation resistance of 100 megohms per mile after three 
minutes' electrification with 550 volts. 

For unlined metal conduits, conductors must conform to 
the specifications given for lined conduits, and in addition 
have a second outer fibrous covering at least one thirty-sec- 
ond of an inch in thickness and sufficiently tenacious to 
withstand the abrasions of being hauled through the metal 
conduit. 



ifAEINE WORK. 297 

h. Must no.t be diawn in until the mechanical work on 
the conduit is completed and same is in place. 

i. Where run through coal bunkers, boiler rooms, and 
where they are exposed to severe mechanical injury, must be 
encased in approved conduit. 

70. Portable Conductors. 

a. Must be made of two stranded conductors each hav- 
ing a carrying capacity equivalent to not less than No. 14 
B. & S. gage, and each covered with an approved insulation 
and covering. 

Where not exposed to moisture or severe mechanical In- 
jury, each stranded conductor must have a solid Insulation 
at least one thirty-second of an inch in thickness, and must 
show an insulation resistance between conductors, and be- 
tween either conductor and the ground, of at least fifty 
meg-ohms per mile after two weeks' submersion in water at 
70 degrees Fahrenheit (21 degrees Centigrade), and be pro- 
tected by a slow-burning, tough-braided outer covering. 

Where exposed to moisture and mechanical injury (as for 
use on decks, holds and fire-rooms) each stranded conductor 
shall have a solid insulation, to be approved, of at least one- 
thirty-second of an inch in thickness and protected by a tough 
braid. The two conductors shall then be stranded together, 
using a jute filling. The whole shall then be covered witli 
a layer of flax, either woven or braided, at least one thirty- 
second of an inch in thickness and treated with a non- 
inflammable waterproof compound. After one week's sub- 
mersion in water at 70 degrees Fahrenheit (21 degrees Centi- 
grade), it must show an insulation between the two con- 
ductors, or between either conductor and the ground, of fifty 
megohms per mile. 

71. Bell or Other wires. 

a. Must never be run in same duct with lighting or power 
wires. 



298 



MODERN ELECTRICAL CONSTRUCTION. 



72. Table of Capacity of Wires. 





Actual 


No. of 


Strands 






Area 




Size of 




B. & S. G. 


C. M. 


Strands. 


B. & S. G. 


Amperes 


19 


1,288 








18 


1.624 


, , 


. . 


3 


17 


2,048 


. . 


, . 


, , 


16 


2,583 


, , 


, , 


« 


15 


3,257 


, , 


, , 


, , 


14 


4407 


. , 


, , 


12 


12 


6,530 


. . 


. , 


17 




9,016 


7 


19 


21 




11,368 


7 


18 


25 




14.336 


7 


17 


30 




18.081 


7 


16 . 


35 




22,799 


7 


15 


40 




30,856 


19 


18 


50 




38.912 


19 


17 


60 




49,077 


19 


16 


70 




60,088 


37 


18 


85 




75,776 


37 


17 


100 




99,064 


61 


18 


120 




124.928 


61 


17 


145 




157.563 


61 


16 


170 




198,677 


61 


15 


200 




250,527 


61 


14 


2S5 




296,387 


91 


15 


270 




373,737 


91 


14 


320 




413,639 


127 


15 


340 



When g-reater conducting area than that of 12 B. Sc S. 
gSige is required, the conductor shall be stranded In a series 
of 7, 19, 37, 61, 91 or 127 wires, as may be required; the 
strand consisting of one central wire, the remainder laid 
around it concentrically, each layer to be twisted in the op- 
posite direction from the preceding. 



73. Switchboard. 

a. Must be made of non-combustible, non-absorptive 
insulating material, such as marble or slate. 

b. Must be kept free from moisture, and must be located 
so as to be accessible from all sides. 

r. Must have a main switch, main cu.t-out and ammeter 
for each generator. 

Must also have a voltmeter and ground detector. 

d. Must have a cut-out and switch for each side of each 
current leading from board. 



MARINE WORK. 299 

e. Must be wired with conductors having an insulation 
as required for moulding or conduit work and covered with 
a substantial flame-proof braid. 

74. Resistance Boxes. 

{^For constrnc^tion rules, .sec No. 60.) 

a. Must be located on switchboard or away from com- 
bustible material. When not placed on switchboard they 
must be mounted on non-inflammable, non-absorptive insulat- 
ing material. 

75. Switches. 

(For construciton rules, see No. 5/.) 

a. When exposed .to dampness, they must be enclosed in 
a water-tight case. 

b. Must be of the knife pattern w^hen located on switch- 
board. 

c. Must be provided so .that each freight compartment 
may be separately controlled. 

76. Cut-Outs. 

(For construction rules, see No. ^j.) 

a. Must be placed at every point where a change is 
made in the size of the wire (unless the cut-out in the 
larger wire will protect the smaller). 

b. In such places as upper-decks, holds, cargo spaces and 
fire-rooms, a water-tight and fireproof cut-out may be used, 
connected directly to mains when such cut-out supplies cir- 
cuits requiring not more than 660 watts energy. 

c. When placed anywhere except on switchboards and 
certain places, as cargo spaces, holds, fire-rooms, etc., where 
it is impossible to run from center of distribution, they must 
be in a cabinet lined with fire-resisting material. 

li. Except for motors, searchlights and diving lamps must 
be so placed that no group of lamps, requiring a current of 
more .than 660 watts, shall ultimately be dependent upon one 
cut-out. 



300 MODERN ELECTKUAL COXSTUUCTION. 

77. Fixtures. 

a. Must be mounted on blocks made from well-seasoned 
lumber treated with two coats of white lead or shellac. 

b. Where exposed to dampness, the lamp must be sur- 
rounded by a vapor-proof globe. 

c. Where exposed to mechanical injury, the lamp must 
be surrounded by a globe protected by a stout wire guard. 

d. Must be wired with same grade of insulation as port- 
able conductors which are not exposed to moisture or mechan- 
ical injury. 

e. Ceiling fixtures over two feet in length must be pro- 
vided with stay chains. 

78. Sockets. 

(For construction rules, see No. 33.) 

79. Wooden Mouldings. 

(For construction rules, see No. 30.) 

a. Where moulding is run over rivets, beams, etc., a back- 
ing strip must first be put up and the moulding secured to 
this. 

b. Capping must be secured by brass screws. 

80. Interior Conduits. 

(For installation rules, see No. 25.) 
(For construction rules, see No. 49.) 

81. Signal Lights. 

a. Must be provided with approved telltale board, located 
preferably in pilot house, which will immediately indicate <i 
burned out lamp. 

82. Motors. 

a. Must be wired under the same precautions as with a 
current of same volume and potential for lighting. The motor 
and resistance box must be protected by a double-pole cut- 
out and controlled by a double-pole switch, except in cases 
where one-quar.ter horse power or less is used. 



MARINE WORK. 301 

The motor leads or branch circuits must be designed to 
carry a current at least 25 per cent greater than that for 
which the motor is rated, in order to provide for the inevitable 
occasional overloading of the motor, and the increased cur- 
rent required in starting, without overfusing the wires, but 
where the wires under this' rule would be overfused, in order 
to provide for the starting current, as in the case of many of 
the alternating current motors, the wires must be of sucli 
size as to be properly protected by these larger fuses. 

In general, motors should preferably have no exposed live 
parts. 

b. Must be thoroughly insulated. Where possible, should 
be set on base frames made from filled, hard, dry wood and 
raised above surrounding deck. On hoists and winches they 
must be insulated from bed-plates by hard rubber, fiber or 
similar insulating material. 

c. Must be covered with a waterproof cover when not 
in use. 

d. Mu&t each be provided with a name-plate giving 
maker's name, the capacity in volts and amperes, and the 
normal speed in revolutions per minute. 

83. Insulation Resistance. 

The wiring in any vessel must test free from grounds ; 
i. e., the complete installation must have an insulation be- 
tween conductors and between all conductors and the 
ground (not including attachments, sockets, receptacles, etc.) 
of not less than the following: 

Up to 25 amperes 800,000 ohms. 

50 •• 400,000 

100 " 200,000 

200 " 100,000 

400 ♦' 50,000 

800 " 25,000 

" 1,600 " 12,500 

All cut-outs and safety devices in place in the above. 
Where lamp sockets, receptacles and electroliers, etc., are 
connected, one-half of the above will be required. 



NEW RULES AND CHANGES IN RULES ADOPTED 

IN "THE NATIONAL ELECTRICAL CODE" 

FOR 1909. 

In the following pages, all of the changes in rules of "The 
National Electrical Code" for the year 1909, are given. It is 
to be noted also that all of the fine print notes of the 1907 
code, which were mainl}- in the form of suggestions, have been 
made mandatory and must now be considered as rules of equal 
standing with the rest. 

CLASS A. 

STATIONS AND DYNAMO ROOMS. 

Fine print note on page 48. beginning 'Tn case of a ma- 
chine," is omitted. 

Fine print note under section d, page 51, beginning "In 
general," is also omitted. 

After section f, page 60, add section g reading, "The use 
of soft rubber bushings to protect the lead wires coming 
through the frames of generators is permitted, except when 
installed where oils, grease, oily vapors or other substances 
known to have rapidly deleterious efifect on rubber, are pres- 
ent in such quantities and in such proximity with motor or 
dynamo as may cause such bushings to be liable to rapid de- 
struction. In such cases hard wood properly filled, or prefer- 
ably porcelain or micanite bushings must be used." 

In place of fine prin^, note page 60 beginning, "Wires from 
generator to switchboard" read: 

"Wires from generator to switchboard may, however, be 
placed in a runway in the brick or cement pier on which the 

302 



NEW RULES AND CHANGES. ^03 

generator stands. When protection against moisture is neces- 
sary, lead-covered cable or iron conduit must be used. 

In place of fine print note under rule b, read : 

Where a number of wires are brought close together, as 
is generally the case in dynamo rooms, especially about the 
switchboard, they must be surrounded with a tight, non-com- 
bustible outer cover. 

Mame proofing must be stripped back on all cables a suf- 
ficient amount to give the necessary insulation distances for 
the voltage of the circuit on which the cable is used. 

Rule c, page 61, is changed to read: 

Must, where not in conduit, be kept so rigidly supported 
that they cannot come in contact. 

Fine print note page 61, beginning ''Voltmeter switches hav- 
ing," is omitted. 

In place of fine print note under a, page 62, beginning 
"Special attention is called," read: 

"Switchboards must not be built up to the ceiling, a space 
of three feet being left, if possible, between the ceiling and 
the board. The space back of the board must be kept free 
of rubbish and not used for storage purposes. 

In place of fine print note tmder c, read : 

"If the wiring is on the back, there must be a clear space 
of at least eighteen inches between the wall and the apparatus 
on the board, and even if the wiring is entirely on the face, 
it is much better to have the board set out from the wall." 

Rule a, concerning resistance boxes and equalizers page 64, 
also part of fine print note on page 65, is changed to read : 

a. Must be placed on a switchboard, or at a distance of at 
least one foot from combustible material, or separated there- 
froni by a slab or panel of non- combustible, non-absorptive, 
insulating material such as slate, soapstone or marble, some- 
what larger than the rheostat, which must be secured in po- 
.^ition independently of the rheostat supports. Bolts for sup- 



304 MODERN ELECTRICAL CONSTKI CTION. 

porting the rheostat shall be countersunk at least y^ inch be- 
low the surface at the back of the slab and filled. 

Fine print note under rule a, ''Lightning arresters," is 
omitted. 

Fine print note under b, beginning, "The switchboard does 
not," is also omitted. 

To rule c, under lightning arresters, page 67, is added : 

"Ground wires for lightning arresters must not be attached 
to gas pipes within the building nor run in iron pipes." 

Fine print note under b, page 69, ''Care and attendance," 
is omitted. 

Rule c and fine print note following under, "Testing of In- 
sulation Resistance," are omitted. 

Fine print note under motors, page ys, beginning, "The use 
of motors," has been changed to read : 

"When motors operating at a potential in excess of 550 
volts are to be installed, it is suggested that plans for such 
installation should be submitted to the inspection department 
having jurisdiction before any work is begun. 

Rule c, under "Motors," page 76, and also fine print note 
following have been changed to read : 

c. Each motor and resistance box must be protected by 
a cut-out and controlled by a switch (see No. 17a), said 
switch plainly indicating whether "on" or "off" (except as 
provided for electric cranes, see 34 A-c). With motors of 
one-fourth horsepower or less, on circuits where the voltage 
does not exceed 300, No. 2id must be complied with, and 
single pole switches may be used as allowed in No. 22c. The 
switch and rheostat must be located within sight of the motor, 
except in cases where ^special permission to locate them else- 
where is given, in writing, by the inspection department hav- 
ing jurisdiction. 

Where the circuit-breaking device on the motor-starting 
rheostat disconnects all wires of the circuit, the switch called 
for in this section mav be omitted. 



NEW liULES AND CHANGES. 305 

Overload-release devices on motor-starling rheostats will 
not be considered to take the place of the cut-out required 
by this section if they are inoperative during tUe starting of 
the motor. 

An automatic circuit-breaker disconnecting all wires of the 
circuit may, however, serve as both s\vitch and cut-out. 

Fine print note under d, page 78, has been changed to 
read : 

Auto starters, unless equipped with tight casings enclosing 
all current-carrying parts, in all wet, dusty or linty places, 
must be enclosed in dust-tight, fireproof cabinets. Where 
there is any liability of short circuits across their exposed live 
parts being caused by accidental contacts, a railing must be 
erected around them. 

Fine print note under f, pages 85-86, has been changed to 
read : 

Such enclosures must be readily accessible, dust proof and 
sufficiently ventilated to prevent an excessive rise of tem- 
perature. Where practicable, the sides should be made largely 
of glass, so that the motor may be always plainly visible. 

The use of enclosed type motor is recommended in dusty 
places, being preferable to wooden boxing. 

Fine print note page 90, beginning, *Tf the insulation,' has 
been omitted. 

CLASS B. OUTSIDE WORK. 

In rule a, page 91, make line seven read: "Support to the 
line, except when run in conduit, may have an approved 
weatherproof." 

In rule b, page 91, make Hue two read: "connection be- 
tween them, and except when run in conduit, not less than 
a foot apart and not." 

To rule b also add: "For conduit work, wires must be 



S06 MODERN ELECTRICAL CONSTRFCTION. 

placed so as to conform to rules for unlined conduit, except 
that conduit system must be waterproof." 

To rule c, 'page 92, add : ''And roof structures must be 
substantially constructed." Omit fine print note under this 
rule entirely. 

Rule d, page 93, is entirely stricken out. 

Rule e has been changed to read : 

e. A'lust, where exposed to the weather, be provided with 
petticoat insulators of glass or porcelain ; porcelain knobs 
or cleats and rubber hooks will not be approved. Wires on 
the exterior walls of buildings must be supported at least 
every fifteen feet, the distance between supports to be short- 
ened if wires are liable to be disturbed. 

Where not exposed to the weather, low potential wires may 
be supported on glass or porcelain knobs which will separ- 
ate the wires at least one inch from the surface wired over, 
supports to be placed at least every four and one-half feet. 

Fine print note under rule g, page 94, has been changed 
to read : 

For low potential systems the service wires may be brought 
into buildings through a single iron conduit. The conduit to 
be equipped with an approved service-head. The inner end 
must extend to the service cut-out. and if a cabinet is re- 
quired by the Code, must properly enter the cabinet. 

Rule a, page 103, has been changed to read: ''AFust not 
be placed inside of any building, excepting central stations 
and sub-stations, except as provided in No. 30A, unless by 
special permission of the inspection department having juris- 
diction." 

Fine print note under rule a, page 103, omitted. 

To rule b, page 103, has been added: "ATust not be at- 
tached to frame buildings when any other location is prac- 
ticable." 



NKW HTI.KS AM) CHANGES. 307 



CLASS C. INSIDE WORK. 



Rules a and b, page no have been changed to read: 

a. Must not be of smaller size than No. 14 B. & S. gauge, 
except as allowed for fixture work and pendant cord. 

b. Tie wires must have an insulation equal to that of the 
conductors they confine. For wire smaller than No. 8 B. 
& S. gauge split knobs or cleats shall be used except at dead 
ends, and tie wires and knobs will not be approved. 

Screws must be used for fastening all cleats and knobs 
which are arranged to grip the wire. 

Rule c, beginning with ''Stranded wires must," has been 
changed to read : 

Stranded wires (except in flexible cords) must be sol- 
dered before being fastened under clamps or binding screws, 
and whether stranded or solid, when the}' have a conduc- 
tivity greater than that of No. 8 B. & S. gauge, they must 
be soldered into lugs for all terminal connections, except 
where an a t> proved solderless terminal connector is used. 

First paragraph of rule d has been changed to read : 

d. ^lust be separated from contact with walls, floors, tim- 
bers or partitions through which they may pass by non- 
combustible, non-absorptive, insulating tubes, such as glass 
or porcelain, except at outlets where approved flexible tubing 
is required. 

Fine print note under rule e, page 120, has been omitted, 
and in its place is : Where tubes are used they must be se- 
curely fastened at the ends to keep them from moving along 
the wire. 

Rule a, page 124, now reads : 

a. On constant potential circuits, all service switches and 
all switches controlling circuits supplying current to motors 
or heating devices, and all fuses, unless otherwise provided 
(for exceptions as to switches see Nos. 8c, 23a and 34A-C; 



303 .M()i)i:i:.\ klkctku'al coNsTurcTioN. 

lor exceptions as to cuts-outs sec No. 21a and b) must be 
so arranged that the fuses wih protect and the opening of 
the switch will disconnect all of the wires; that is, in the 
two-wire system the two wires, and the three-wire S3'stem 
the three wires, must be protected by the fuses and discon- 
nected by the operation of the switch. 

When installed without other automatic overload protect- 
ive devices automatic overload circuit breakers must have 
the poles and trip coils so arranged as to afford complete 
protection against overloads and short circuits, and if also 
used in place of the swntch must be so arranged that no one 
pole can be opened manually without disconnecting all the 
wires. 

This, of course, does not apply to the grounded circuit of 
street railway systems. 

Rule d, page 127, is shortened and now reads: 'Time 
switches, sign flashers and similar appliances must be of ap- 
proved design and enclosed in approved cabinet." 

CONSTANT CURRENT SYSTEMS. 

rine print note on page 132, beginning, ''Except on joisted," 
has heQu omitted. 

CONSTANT POTENTIAL SYSTEMS. 

Fine print note on page 134, beginning, "Excepting on 
main switchboard," has been omitted. 

Rule a, page 136, has been changed to read: 

a. Must be placed on all service wires, either overhead or 
underground, in the nearest accessible place to the poi!it 
where they enter the building and inside the walls, and ar- 
langed to cut off the entire current from the building. 

From rule c, page 144, reference (see No. 54) has been 
omitted and fine print note has been changed to read : "Link 
fuses must be used only when mounted on approved slate 



NEW RULES AND CHANCES. 309 

or marble bases, and must be enclosed in dust-ligiil, hreproof 
cabinets, except on switchboards. 

Fine print note on page 145, beginning, "The idea is to," 
has been omitted. 

To rule e on page 146 add : 'Tn which event the circuit- 
breaker may be set as high as 100 per cent above such ca- 
pacity." 

Following rule e, add rule f, as follow^s : 

f. Each phase of A. C. motor circuits, except on main 
switchboard or when otherwise subject to expert supervision, 
must be protected by an approved fuse whether automatic 
overload circuit-breakers are installed or not. Single phase 
motors may have one side protected by an approved auto- 
matic overload circuit-breaker only if the other side is pro- 
tected by an approved fuse. For circuits having a maximum 
capacity greater than that for which enclosed fuses are ap- 
proved circuit-breakers alone will be approved. 

Paragraphs i and 2 of fine print note on page 147 now 
read : 

When practicable, switches must be so wired that blades 
will be "dead" when switch is open. 

When switches are used in rooms where combustible fly- 
ings would be likely to accumulate around them, they must 
be enclosed in dust-tight cabinets." 

To rule f, page 152, add: "Or they may be omitted if the 
switch is approved for mounting -directly on the moulding. 

On page 153 omit fine print note beginning, "An approved 
automatic." 

LOW POTENTIAL SYSTEMS. 

550 volts or less. 

Rule a has been chano^ed to read : 

a. Where entering cabinets must be protected by approved 
bushings, which fit tightly the holes in the box and are well 



310 M0L)J:KN ELECTKICAL CONSTKrCTION. 

secured in place. The wires should completely till the holes 
in the bushings so as to keep out the dust, tape being used 
to build up the wires if necessary. On concealed knob and 
tube work approved flexible tubing will be accepted in lieu 
of bushings, providing it shall extend from the last porce- 
lain support into the cabinet. 

To rule h, page 159, add: "]^Iust not be dead-ended at 
a rosette socket or receptacle unless the last support is 
within twelve inches of the same." 

Rule k, page 163, has been changed to read : 

k. Must have an approved rubber insulating covering, and 
m.ust be in continuous lengths from outlet to outlet, or from 
fitting to fitting, no joints or taps to be made in moulding. 
Where branch taps are necessary in moulding work approved 
fittings for this purpose must be used. 

Fine print note under i, page 163, has been omitted. 

Fine print note, page 168, beginning, 'The same conduit," 
lias been changed to read : 

The same conduit must not contain more than four two- 
wire, or three three-wire circuits of the same system, except 
by special permission of the inspection department having 
jurisdiction, and must never contain circuits of different sys- 
tems. 

Rules t and u, page 170, have been changed to read: 

t. When using either conduit or armored -cable in mixed 
concealed knob and tube work, the requirements for conduit 
work or armored cable work must be complied with as the 
case may be. 

u. ]\Iust at all outlets, except where conduit is used, be 
protected by approved flexible tubing, extending in continu- 
ous lengths from the last porcelain support to at least one 
inch beyond the outlet. In the case of combination fixtures 
the tubes must extend at least flush with outer end of gas 
cap. 



>-EW KULES AND CHANGES. 3U 

When the surface at any outlet is broken, it must be re- 
paired so as to leave no holes or open spaces at such out- 
let. It is suggested that approved outlet boxes or plates be 
installed at all outlets in concealed "knob and tube" work, 
the wires to be protected by approved flexible tubing, ex- 
tending in continuous lengths from the last porcelain support 
into the box. 

To rule v, page 173, has been added: In wiring certain 
designs of show-case fixtures, ceiling bulls-eyes and similar 
appliances in which the wiring is exposed to temperatures 
in excess of 120 degrees Fahrenheit (49 degrees Centigrade), 
from the heat of the lamps, approved slow-burning wire may 
be used. All such forms of fixtures must be submitted for 
examination, test and approval before being introduced for 
use. 

Rule y, page 173, has been changed to read: 

y. Wires of different systems must never be contained in 
or attached to the same fixture and under no circumstances 
must there be a difference of potential of more than 300 volts 
between wires contained in or attached to the same fixture. 

From note under a, page 173. the word "underground" has 
been omitted. 

Fine print note under c, page 174, has been changed to 
read : 

Armor of cables and gas pipes must be securely fastened 
in metal outlet boxes so as to secure good electrical connec- 
tion. W^here boxes used for centers of distribution do not 
afford good electrical connection the armor of the cables 
must be joined around them by suitable bond wires. Where 
sections of armored cable are installed without being fastened 
to the metal structure of buildings or grounded metal piping, 
they must be bonded together and joined to a permanent and 
efficient ground connection. 

Rule d, page 174, has been changed to read: 



312 MODEllX ELECTKICAL CONSTKLCTIUN. 

d. When installed in so-called fireproof buildings in course 
of construction or afterward if exposed to moisture, or 
where it is exposed to the weather, or in damp places such 
as breweries, stables, etc., the cable .must have a lead cov- 
ering at least one thirty-second inch in thickness placed be- 
tween the outer braid of the conductors and the steel armor. 

The lead covering is not to be required when the cable 
is run against brick walls or laid in ordinary plaster walls 
unless same are continuously damp. 

On page 174, following g, rule h has been added. 

h. All bends must be so made that the armor of the cable 
will not be injured. The radius of the curve of the inner 
edge of any bend not to be less than i^ inches. 

Fine print note under "Interior Conduits" has been omit- 
ted. 

Fine print note under f, page 180, has been changed to 
read: 

Conduits and gas pipes must be securely fastened in metal 
outlet boxes so as to secure good electrical connection. If 
conduit, couplings, outlet boxes or fittings having protective 
coating of non-conducting material, such as enamel, are used, 
such coating must be thoroughly removed from threads of 
both couplings and conduit and from surfaces of boxes and 
fittings where the conduit is secured in order to obtain the 
requisite good connection. Where boxes used for centers 
of distribution do not afYord good electrical connection, the 
conduits must be joined around them by suitable bond wires. 
Where sections of metal conduit are installed without being 
fastened to the metal structure of buildings or grounded 
metal piping, they must be bonded together and joiucd to 
a permanent and efficient ground connection. 

To fine print note under rule d, pages 186-187. has hern 
added: "It is suggested that outlet boxes and fitting? hav- 
ing conducting coatings be used in order to secure better 



NEW KULES AM) CHANGES. 313 

electrical contact at all points throughout the conduit sys- 
tem." 

To rule a, page 187, has been added : 

In straight electric fixtures where the insulation of con- 
ductors and the metal of fixtures are the equivalent of a 
conduit or armored cable system, or where used with ap- 
proved wireless clusters or where the double-braided wire 
extends directly into an approved porcelain socket, the in- 
sulating joint may be omitted. 

Rule c, page 190, has been changed to read : 

"Must be free from contacts between conductors and fix- 
tures, 'short circuits' and ground connection, and must be 
tested for such conditions before being connected to the cir- 
cuit supply conductors." 

Following rule d, page 193, the following have been added : 

e. The so-called fiat canopy sometimes used on electric 
and combination fixtures will not be approved except in 
connection with outlet boxes. 

f. Must, when installed on the outside of frame buildings, 
be of water-tight construction. 

g. Must not, when wired on the outside, be used in show 
windows or in the immediate vicinity of especially iniiam- 
mable stuff. 

In place of fine print note, page 195, the following is sub- 
stituted : 

''For all portable work, including those pendants which are 
liable to be moved about sufficiently to come in contact with 
surrounding objects, flexible wires and cables especially de- 
signed to withstand this severe service must be used. 

When necessary to prevent portable lamps from coming in 
contact with inflammable materials, or to protect them from 
breakage, they must be surrounded with a substanti.il wire 
guard. 

Rule e, page 196, has been changed to read: ''^lu^t r.ot 



314 MODEKX KLECTIUCAL CONSTRUCTION. 

be used in show windows or showcases, except when pro- 
vided with an approved metal armor. 

NEW RULE. 
29A. MERCURY VAPOR LAMPS. 

Enclosed Mercury Vapor Lamps. 

a. ^lust have cut-out for each lamp or series of lamps, 
except when contained in single frame and lighted by a 
single operation, in which case not more than live lamps 
should be dependent upon single cut-out. 

b. Must only be furnished with such resistances or regu- 
lators as are enclosed in non-combustible cases, such resist- 
ances to be treated as sources of heat. In locations where 
these resistances or regulators are subject to flyings of lint 
or combustible material, all openings through cases must be 
protected by fine wire gauze. 

HIGH POTENTIAL VACUUM TUBE SYSTEMS. 

c. The tube must be -o installed as to 1)e free from me- 
chanical injury or liability to contact with inflammable ma- 
terial. 

d. High potential coils and regulating apparatus must be 
installed in approved steel cabinet not less than t-to inch 
in thickness ; same to be well ventilated in such a manner 
as to prevent the escape of any flame or sparks, in case of 
burnout in the various coils. All apparatus in this box must 
be mounted on slate* base and the enclosing case positively 
grounded. Supplying conductors leading into this high po- 
tential case to be installed in accordance with the standard 
requirements governing low potential systems, where such 
wires do not carry a potential of over 300 volts. 



NEW KULES AND CHANGES. 315 

NEW RULE. 
3OA. TRANSFORMERS. 

Oil Transformers. 

a. Must not be placed inside of any building except cen- 
tral stations and sub-stations, unless by special permission of 
the inspection department having jurisdiction. 

Air-Cooled Transformers. 

The folloz^'ing sections do not ap/^ly to apparatus or fit- 
tings, the operation of i^'hieh depends either Zij'holly or in 
part upon special transformers embodied in the devices, but 
all such apparatus or fittings must be submitted for special 
examination and approval before being used. 

b. Must not be placed inside of any 1)uilding excepting 
central stations and sub-stations, if the highest voltage of 
either primary or secondary exceeds 550 volts. 

c. Must be so mounted that the case shall be at a distance 
of at least one foot from combustible material or separated 
therefrom by non-combustible, non-absorptive, insulating ma- 
terial, such as slate, marble or soapstone. This will require 
the use of a slab or panel somewhat larger than the trans- 
former. 

Fine print note on page 199, beginning, "No System of,'' 
is omitted. 

THEATRE WIRING. 

All rules requiring conduit exclusively have been changed 
to admit armored cable. 

Rule e and fine print note on page 207 have been changed 
to read : 

c. Cables must be made up of approved, stranded rubber- 
covered wires; conduit construction must be used from 
switchboard to point where cables must be flexible to per- 



316 MUDEIi.X ELECTltlCAL CUMSTKUCTION. 

niit of the raising and lowering of border, and flexible por- 
tion must be enclosed in an approved fireproof hose or braid 
and be suitably supported. 

An approved junction box must be installed at the end of 
the conduit where the liexible cable leaves for the border. 

Rule c, page 215, has been changed to read: 

1. ''Must be wired in approved conduit or armored cable.'* 

2. All pendant lamps must be equipped with approved re- 
inforced cord, armored cable or steel armored flexible cord. 

3. All lamps must be provided with approved guards. 
Rule e, page 224, section i, has been changed to read: 

''All wiring must be installed in approved conduit or arm- 
ored cable." 

NEW RULE. 
3IB. OUTLINE LIGHTING. 

Wiring (other than signs on exterior of buildings) : 

a. Must be connected only to low-potential systems. 

b. Open or conduit work may be used, but molding will 
not be permitted. 

c. For open work, wires must have an approved rubber 
insulating covering. Must be rigidly supported on non-com- 
bustible, non-absorptive insulators, which separate the wires 
at least one inch from the surface wired over, and must be 
kept apart at least two and one-half inches for voltages up 
to 300, and four inches for higher voltages. 

Rigid supporting requires, under ordinary conditions where 
wiring over flat surfaces, supports at least every four and 
one-half feet. Tf the wires are liable to be disturbed, the 
distances between sup*ports should be shortened. 

d. Where flexible tubing is required, the ends must be 
sealed and painted with moisture repcllant, and kept at least 
one-half inch from surface wnred over. 

e. Wires for use in ri.o^id or flexible steel conduit must 



NEW ItlLKS AM) CHANGES. 317 

:oniply with requirements lor unlined coiuluit work. Whtrc 
armored cable is used, the conductors must be protected from 
moisture by lead sheath between armor and insulation. 

f. Must be protected by its own cut-out, and controlled 
by its own switch. Cut-outs, switches, time switches, flash- 
ers and similar appliances, must be of approved design, and 
must, if located inside the building, be installed as required 
by the code for such devices. If outside the building they 
must be enclosed in a steel or cast-iron box. 

If a steel box is used, the minimum thickness of the steel 
must be 0.128 of an inch (No. 8 B. & S. gauge). 

Boxes must be so constructed that when switch operates 
the blade shall clear the door by at least one inch, and 
they must be moisture proof. 

h. Circuits must be so arranged that not more than 1,320 
watts will be finally dependent upon a single cut-out ; nor 
shall more than 66 sockets or receptacles be connected to 
single circuit. 

i. Sockets and receptacles must be of the keyless porcelain 
type, and wires must be soldered to lugs on same. 

To section 4 of rule b, page 226, add : "Except that when 
motors are so enclosed that flame cannot extend outside of 
the casing, the flame proof covering will not be required on 
the motor leads." 

Section 6, rule b, page 227, has been changed to read : 

6. All connections of cables to cut-outs, switches and fit- 
tings, except those to controller connection boards, when de- 
signed to carry over 25 amperes, must be provided with lugs 
or terminals soldered to the cable, and securely fastened to 
the device, by bolts, screws or by clamping; or, the end of 
the cable, after the insulation is removed, shall be dipped in 
solder and be fastened into the device by at least two set 
screws having check nuts. 

x\ll connections for conductors to fittino-s. etc., desiorned 



318 MODETJX ELECTRICAL COXSTUrCTION. 

to carry less than 25 amperes, must be provided with up- 
turned lugs that will grip the conductor between the screw 
and the lug, the screws being provided with flat washers ; or 
by block terminals having two set screws, and the end of the 
conductors must be dipped in solder. Soldering, in addition 
to the connection of the binding screws, is strongly rec- 
ommended, and will be insisted on wdien above requirements 
are not complied with. 

This rule only to apply to circuits where the maximum 
potential is over 25 volts and current exceeds 5 amperes. 

Rule f, page 229, has been changed to read : 

"i. Each outlet to be provided with an approved recep- 
tacle, or an approved cluster. No lamp consuming more 
than 128 w^atts to be used." 

To rule g, page 230, add : 

Truss plank heaters to be mounted on not less than one- 
quarter inch fire-resisting insulating material, the legs or 
supports for the heaters providing an air space of not less 
than one-half inch between the back of the heater and the 
insulating material. 

CAR HOUSES. 

Section 3, of rule e, page 234, has been changed to read : 
3. Must have all rails bonded at each joint with a con- 
ductor having a carrying capacity at least equivalent to No. 
o B. & S. gauge annealed copper wire, and all rails must 
be connected to the outside ground return circuit by a not 
less than No. o B. & S. gauge copper wire or by equivalent 
bonding through the track. All lighting and stationary 
motor circuits must be thoroughly and permanently con- 
nected to the rails or to the wire leading to the outside 
ground return circuit. 

No. 34 has been changed as follow^s : 



319 NEW RULES AND CHANGES. 

34. LIGHTINC; AND TOWER FROM RAILWAY WIRES. 

a. Must not be permitted, under any pretence, in the same 
circuit with trolley wires with a ground return, except in 
electric railway cars, electric car houses, power houses, pas- 
senger and freight stations connected with the operation of 
electric railways. 

34A. ELECTRIC CRANES. 

All zciri)ig, apparatus, etc., not spcciUcaUy covered by spe- 
cial rules herein given, must conform to the Standard Rides 
and Requirements of the National Electrical Code, except 
that the sicitch required by Rule 8c for each motor may be 
omitted. 

A. WIRING. 

1. All wires except bare collector wires, those between re- 
sistances and contact plates of rheostats and those subjected 
to severe external heat, must be approved, rubber-covered 
and not smaller in size than No. 12 B. & S. Insulation on 
wires between resistances and contact plates of rheostats 
must conform to Section d, while wires subjected to severe 
external heat must have approved slow-burning insulation. 

2. All wires excepting collector wires and those run in 
metal conduit or approved flexible cable must be supported 
by knobs or cleats which separate them at least one inch 
from the surface wired over, but in dry places where space 
is limited the distance between wires as required by Rule 
24-h cannot be obtained, each wire must be separately en- 
cased in approved flexible tubing securely fastened in place. 

Collector wires must be supported by approved insulators 
so mounted that even with the extreme movement permitted 
the wires will be sepa;rated at all times at least i 1-2 inches 
from the surface wired over. Collector wires must be held 
at the ends by approved strain insulators. 



320 MODEKN ELECTllICAL CONSTKUCTION. 

3. Main collector wires carried along the runways must be 
rigidly and securely attached to their insulating supports at 
least every 20 feet, and separated at least six inches when 
run in a horizontal plane ; if not run in a horizontal plane, 
they must be separated at least 8 inches. If spans longer 
than 20 feet are necessary the distance between wires must 
be increased proportionately but in no case shall the span ex- 
ceed 40 feet. 

4. Where bridge collector wires are over 80 feet long, in- 
sulating supports on which the wires may loosely lie must be 
provided at least every 50 feet. 

Bridge collector wires must be kept at least 2 1-2 inches 
apart, but a greater spacing should be used whenever it may 
be obtained. 

5. Collector wires must not be smaller in size than speci- 
fied in the following table for the various spans. 

Distance between Size wire 

rigid supports. required. 

Feet. ^ B. & S. 

o to 30 6 

31 to 60 ' 4 

Over 60 2 

B. COLLECTORS. 

Must be so designed that sparking between them and 
collector wires will be reduced to a minimum. 

C. SWITCHES AND CUT-OUTS. 

1. The main collector wires must be protected by a cut- 
out and the circuit* controlled by a switch. Cut-out and 
switch to be so located as to be easy of access from the 
floor. 

2. Cranes operated from cabs must have a cut-out and 
switch connected into the leads from the main collector 



NEW KULES AND CUANOES. 32) 

wires and so located in the cab as to be readily accessible 
to the operator. 

3. Where there is more than one motor on a single crane, 
each motor lead must be protected by a cut-out located in 
the cab if there is one. 

D. CONTROLLERS, 

Must be installed according to No. 4, except that if the 
crane is located out doors the insulation on wires between 
resistances and contact plates of rheostats must be rubber 
where the wires are exposed to moisture and insulation is 
necessary and also where they are grouped. If the crane 
operates over readily combustible material, the resistances 
must be placed in an enclosure made of non-combustible 
material, thoroughly ventilated and so constructed that it will 
not permit any flame or molten metal to escape in the event 
of burning out the resistances. If the resistances are located 
in the cab, this result may be obtained by constructing the 
cab of non-combustible material and providing sides which 
enclose the cab from its floor to a height at least 6 inches 
above the top of the resistances. 

E. GROUNDING OF IRON WORK. 

The motor frames, the entire frame of the crane and the 
tracks must be permanently and effectively grounded. 

HIGH POTENTIAL SYSTEMS. 

To preliminary note page 234 has been added : "For 550 
volt motor equipments a margin of ten per cent above the 
550 volt limit will be allowed at the generator or trans- 
former without coming under high potential systems." 

CLASS E. MISCELLANEOUS. 

Rule b, page 288, has been changed to allow separation of 
wires to be 24 inches instead of 26, 



322 MODEKX ELF.CTRICAL CONSTRUCTION. 

Above rule c, page 288, has been inserted : 'When the wires 
are carried in approved cables the next three sections c, d and 
e do not apply." 

Rule d, page 288, has been changed by omitting last line 
reading : ''Except when brought in through approved metal 
covered cables." 

Paragraph 2, of section 3, rule 7, page 290, has been 
changed to read : 

When the ground wire is attached to a water pipe or a gas 
pipe, it may be connected by means of an approved ground 
clamp fastened to a thoroughly clean portion of said pipe, or 
the pipe shall be thoroughly cleaned and tinned with rosin 
flux solder, and the ground wire shall then be wrapped 
tightly around the pipe and thoroughly soldered to it. 

Paragraph 3, in same rule has been entirely omitted. 

Rule n, page 292, has been changed to read : 

n. Wires beyond the protector, or wires inside buildings 
where no protector is used, must be neatly arranged and 
securely fastened in place in some convenient, workmanlike 
manner. 

They must not come nearer than three inches to any elec- 
tric light or power wire in the building, unless separated 
therefrom by some continuous and firmly fixed non-con- 
ductor creating a permanent separation ; this non-conductor 
to be in addition to the regular insulation on the wire. 

Fine print note at bottom of page 292 has been omitted. 



PRACTICAL HINTS. 323 

PRACTICAL HINTS. 

A full description of the Wheatstone bridge, the telephone, 
magneto and other instruments, as well as the many ways of 
their application in testing for defects and for circuits in elec- 
trical installations having been given in a previous work of the 
authors (Wiring Diagrams and Descriptions) it is not thought 
necessary to repeat them here, especially as a work of this 
kind is necessarily limited m diagrams which would be re- 
quired to a full understanding of methods. This chapter will, 
therefore, consist only of such hints and instructions as apply 
to general work. 

An electric light circuit may be tested for "short circuit" by 
connecting an incandescent lamp in place of one of the fuses. 
If the lamp burns while there are no lamps in circuit, there is 
sure to be a short circuit. A low candle-power lamp will indi- 
cate with less current than a high-candle-power lamp and is, 
therefore, better. If no lamp is available a small fuse should 
first be tried. 

A test for "ground" may be made in the same way, but the 
lamp must be connected to both sides in turn and the fuse left 




oc^ooooc:)^^-^^^ 



Figure 168 

out. If the main system to which the circuit to be tested con- 
nects is not grounded, a temporary ground must be put on. 
This is best done by connecting a lamp with one wire to a gas 
or water pipe and the other to the ''live" binding screw on the 
opposite side of cutout to that in which the other lamp is con- 
nected. Thus, in Figure 168, if a ground should exist at 3 and 
the lamp be connected to gas pipe, as shown, the test lamp at 1 
would burn. 



324 MODERN ELECTRICAL CONSTRUCTION. 

If a voltmeter were connected in place of (Mther of the 
lamps, the test would be much more searching. 

With 3-wire systems no ground need be put on, as the neu- 
tral wire will always be found grounded. The lamp need be 
tried in the outside fuses only. This test will be more search- 
ing if lamps are placed in all sockets connected. 

In placing fuses in the 3-wire, 110-220 volt system, the neu- 
tral wire should always be fused lirst. 

By reference to Figure 169 it will be seen that while the 
neutral fuse in main blocks a is out, the two circuits of lamps 
c and d must burn in series; that is, just as much current must 
pass through one circuit as through the other. So long as 
there is an equal number of lamps in each circuit there is no 
trouble; but should most of the lamps in one circuit be turned 
off, those remaining would have to carry all the current that 
passes through the lamps of the other circuit. This current 
would overheat them and break, or burn them out in a very 
short time. If the neutral fuse is in place, each circuit is inde- 
pendent of the other and the neutral wire only carries the 
difference m current between the two sets of lamps. In order 
to insure against a neutral fuse "blowing" first in case of 
trouble, it is generally made heavier than in the outside wires. 
When a 3-w^ire circuit is to be cut off, the outside fuses should 
be drawn first. 

In order to find which is the "neutral" wire, two 110 volt 
lamps are connected in series and the wires from them brought 
in contact with two of the three wires. If both lamps burn at 
full candle power we have 220 volts, which is the pressure of the 
outside wires, and, \herefore, the other wire must be the neu- 
tral. If the lamps burn only at half candle power, we have 
only 110 volts and one of the wires must be the neutral. That 
wire which gives 110 volts with either one of the other two 
wires is the neutral; this wire should always be run in the 
center between the other two. 



PRACTICAL HINTS. 



325 



A test for the neutral wire can also be made by connecting 
a lamp to ground. A lamp connected this wa}^ will burn from 
either of the outside wires, but not from the neutral. 

If the neutral wire should be connected to any but the 
middle binding post of 3-wire cutouts and the uutside wire 
to the other two, one-half of the lamps would be almost imme- 
diately destroyed, being subject to 220 volts, while the other 
half would burn properly. 

If a short circuit occurs, say. at e, Figure 169, on one side 
of a 3-wire system and blows the neutral fuse on that side of 
the circuit, we shall have 220 volts on the lamps on the oppo- 
site side. This will quickly burn them out. Most of these 



COOP 




j O j^O o"'^-^ 



Figure 169 



troubles are avoided to some extent by the use of such branch 
cutouts as shown. This confines trouble of this kind to the 
mains. 

On any system having a neutral wire or a wire on one side 
grounded, if a ground on either of the other wires occurs, the 
trouble can be temporarily remedied by simply changing the 
two wires of that circuit at the cutout. This will trans- 
fer the ground to the side already grounded, so that it will 
not interfere with operation. The ground must, however, be 
cleared up at once as no grounding is ever allowed inside of 
any building. 

When strip cutouts are set horizontally and there is no 



326 MODERN ELECTRICAL CONSTRUCTION. 

bridge between opposite polarities, there will be the possibility 
of a partially melted upper fuse sagging down and forming a 
short circuit. 

On panel boards where fuses are set too close together, the 
heat of one fuse while blowing will often blow the next fuse 
above it. 

If large fuses are enclosed in small and very tight cabi- 
nets, the vapors formed by blowing will often cause short 
circuits. 

Before installing fuses in a ''loaded" circuit, it is advisable 
to disconnect as many lights and other devices as possible. If 
there is a main switch this can easily be done. If there is no 
such switch on that part of the system, the task of placing 
fuses is somewhat hazardous; for at the very instant that the 
second fuse touches its terminal a great rush of current will 
flow. If there happens to be a "short" on the line both fuses 
will probably blow and may burn the operator's hands anoi 
face severely. In order to avoid this, extremely careful manip- 
ulation is necessary. The first fuse can be placed without 
any difficulty, as there will be no current flow unless the cir- 
cuits are grounded. Before attempting to place the second 
fuse the circuits may be tested for "shorts" by placing a 
"jumper" (a piece of wire heavy enough so that it will not 
be heated by the current it is to carry) with the ends on the 
other fuse terminals. This "jumper" will complete the cir- 
cuit and, if all is in order the lights will burn. If there are 
two men, one may hold the jumper while the other places the 
fuse, but it should be placed as quickly as possible, especially 
if the circuit has a motor load, for these will be started very 
soon after the lights* come on and will greatly increase the 
current. If there is but one man the jumper may be tem- 
porarily fastened to the mains. 

A jumper is not absolutely necessary even with large fuses, 
for if the last contact is made quickly and held steady, there 



PRACTICAL HINTS. 



327 



will be very little arcing; one should, however, provide all pro- 
tection possible. If a piece of asbestos is at hand, it may be 
used to cover the fuses, so as to protect the hands and face 
from melted metal. 

Before attempting to re-fuse a circuit, note condition of 
cutout block. If there is evidence of a great flash, it is very 
likely that the fuse was blown by a short circuit. If the 
blowing was caused by a slight overload or loose contact, the 
destructive effect will be much less. 

Much trouble can be prevented by cleaning terminals of 
fuse blocks occasionally and going over nuts and screws to 
see that they are tight. 

In Figure 170, a shows the proper way of connecting small 
wires into such terminals. This method prevents the screw 
from cutting into the main wire and allowing it to break. 

A wire should always be bent around the binding post of 
switch or cutout in the direction in which the nut which is to 





Figure 170 



hold it must turn to be fastened as in c. If a wire is not long 
enough to be bent around the post or screw, a small piece of 
wire should be placed opposite it so as to give a level bearing 
to nut or washer. See b. 

Plug cutouts having their metal parts projecting above the 
porcelain, as shown at d, should be connected, whenever pos- 
sible, so that these metal parts are dead when fuses are with- 
drawn. This will prevent many accidental short circuits. 

The positive and negative wires of a circuit can easily be 
determined by immersing both wires in a little water, keeping 



328 MODERN ELECTRICAL CONSTRUCTION. 

them an inch or so apart. Small bubbles will soon appear at 
the negative wire. 

If an arc lamp has been properly connected, the upper car- 
bon will be heated much more than the lower and will remain 
red longer. An arc lamp improperly connected is said to be 
burning "upside down" and will at once manifest itself by the 
strong light thrown against the ceiling. 

It is very often found necessary to determine the capacity 
of a cable which is already installed and w^here it is impossible 
to get at the separate wires of which it is formed. As cables 
are usually made up in a uniform manner, as shown in the 
table below, their capacity can be determined by the following 
method : To find the number of circular mils in a cable made 
up of wires of uniform size. Measure diameter of cable, 
count number of wires in outside layer, and, referring to the 
table below, find the same number in the first column ; divide 
the diameter of cable by the number set opposite this in the 
second column. This will give the diameter of each wire. 
Multiply this diameter by itself and then by the number of 
wires contained in cable as given in the third column. All 
measurements should be expressed in mils (1/1,000 inch) and 
the result wall be the circular mils contained in cable. 

Outside layer 6 wires 3 times diameter 7 wires in cable 



12 
18 
24 
30 
36 
42 



5 " " 19 

7 " " 37 

9 " " 61 

11 " " 91 

13 " " 127 

15 " " 169 



The various figures in Figure 171 are designed to show how 
many single wires may be run in one conduit. Under each 
figure is given a number which, if multipled by the diameter 
of the wire to be used will give the smallest diameter of 
tube which can contain the corresponding number of 
wires. Thus, for instance, if 12 wires are run through 



PRACTICAL HINTS. 



329 




330 MODERN ELECTRICAL CONSTRUCTION. 

one tube or conduit, the diameter of that conduit 
must be at least 4 1/3 times as great as the diame- 
ter of the wire to be used. Each figure ilkistrates 
the amount of spare room the corresponding number of wires 
leave, and it is necessary to use considerable judgment. Long 
runs will require more space, especialh^ if the wires be quite 
large. Much also depends upon the nature of the insulation 
and the temperature. The figures are believed to be correct 
for single wires and can be followed for twin wires, as the 
same number of conductors arranged that way will not occupy 
as much space as single wires. The actual diameter of lined 
and unlined conduits are given in another table and may be 
referred to. The best way to accurately determine the diam- 
eter of small wire consists in cutting a number of short pieces 
and laying them together, then measuring over all and divid- 
ing the measurement by the number of wires. 



TRICKS OF THE TRADE. 

Cases have been known where it was requested to replace 
single pole switches by double pole, that the single pole switch 
was replaced as requested, but, instead of running both wires 
through it as required, only one wire had been properly 
brought into it and the other two binding posts filled out with 
short pieces of wire calculated to deceive the inspector. A 
test to detect this without disconnecting the switch is easily 
made. By reference to Figure 172 it will be seen that if a 
double pole snap switch is properly connected, current can 
be felt if the points a and b are touched with moistened fin- 
gers. If the switch is connected single pole, current can be 
felt at b and c, when the switch is open, only. 

On one occasion a wireman had run some wires on insu- 
lators along a ceiling and instead of soldering joints had care- 



TRICKS OF THE TRADE. 331 

fully, in many places above the joints, smoked the ceiling with 
a candle in order to deceive an inspector. 

In several cases where an "over-all" test of insulation re- 
sistance was made, meter loops which had been run in con- 
tinuous pieces were found with the wire "nicked" with a knife 
and then broken, leaving the insulation nearly intact, but the 
circuit open. A similar trick is often worked with the ground 
wire of ground detectors. 

In other cases plugs with fuses removed were put in 
"bad" circuits. In one case the real circuit wires (concealed 





Figure 172 Figure 173 

work) were disconnected from cutouts and pushed back into 
the wall and short pieces connected instead. 

In another case where wire not up to requirements had 
been used and condemned, this wire, being run between joists 
and concealed by plastering, was pushed back and short 
pieces of approved wire stuck in at outlets. 

Sometimes in fished work after inspection the long 
pieces of loom reaching from outlet to outlet are withdrawn 
and short pieces at the outlets substituted. 

Lamp butts with wire terminals twisted together, or a 
strand of wire from lamp cord twisted around the base as 
shown in Figure 173 and screwed into the cutout are often 
used in place of fuses. The strand of cord is sometimes used 
to help out a fuse plug on an overloaded circuit. 



3H2 MODERN ELECTRICAL CONSTRUCTION. 

Table of Carrying Capacity of Wires. 

The following table, showing the allowable carrying ca- 
pacity of copper wires and cables of ninety-eight per cent con- 
ductivity, according to the standard adopted by the American 
Institute of Electrical Engineers, must be followed in placing 
interior conductors. 

For insulated aluminum wire the safe carrying capacity 
is eighty-four per cent of that given in the following tables 
for copper wire with the same kind of insulation 

TABLE NO. I. 



;. & s. G. 

18... 
16. . . 
14. . . 


Table A. 

Rubber 

Insulation. 

See No. 41. 

Amperes. 

3. .. . 

6 

12. . . . 


Table B. 

Other 
Insulations. 
SeeNos. 42 to 44. 
Amperes. Circular Mils, 

5 1,624 

8 2,583 

. . . . 16 4.107 


12. . . 
10. .. 

8. . . 


17 

24 

. . . 33 


23. . . 

32. .. 

46. . . 


..... 6,530 

10,380 

16,510 


6... 
5... 
4. . . 


46... . 

54 

65. . . . 


. ... 65... 
.... 77... 
92. . . 


. 26,250 

' 33,100 

41,740 


3. . . 


76 

90 

. ... . 107.... 
. . . . 127 


. . . . 110. . . 


. . . . . 52,630 


2. . . 
1. . . 


.... 131... 
. . . . 156. . . 


66,370 

83,690 


0. . . 


. . 185. . . 


105,500 


00. . . 


150. . . . 


220. . . 


133,100 


000. .. 
0000. .. 


177 

210 


262. . . 

. . . . 312. . . 


167,800 

211,600 



Circular Mils. 

200,000.. 200 300 

300,000 270 400 

400,000 330 500 

500,000 390 590 

600,000 450 680 

700,000 500 760 

800,000 550 840 

900, 000. s 600 920 

1,000,000 65.0 1,000 

1,100,000 690 1,080 

1,200,000 \ 730 1,150 

1,300,000 770 1,220 

1,400,000 810 1,290 

1,500,000 850 1,360 

1,600,000 890 1,430 

1,700,000 930 1,490 

1,800,000 970 1,550 

1,900,000 1,010 1,610 

2,000,000. ... 1,050 1,670 



TABLES. 383 

The lower limit is specified for rubber-covered wires to 
prevent gradual deterioration of the high insulations by the 
heat of the wires, but not from fear of igniting the insulation. 
The question of drop is not taken into consideration in the 
above tables. 

The carrying capacity of Nos. 16 and 18, B. & S. gage wire 
is given, but no smaller than No. 14 is to be used, except as 
allowed under Nos. 24 v and 45 b. 



WIRING TABLES. 

The wiring tables, II-VI, are arranged in the following 
manner : For each size of wire and voltage considered there 
is given (under the proper voltage and opposite the number 
of the wire under the heading B. & S.) the distance it will 
carry 1 ampere at a loss designated at top of page. 

The same wire will carry 2 amperes only half as far at the 
same percentage of loss and again will carry I ampere twice 
as far at double the percentage of loss. 

From these facts we deduce the rule of these tables, which 
is: Multiply the distance in feet (one leg only) by the num.- 
ber of amperes to be carried. Take the number so obtained 
and under the proper voltage find the number nearest equal to 
it. Opposite this number, under the heading B. & S., will be 
found the size of wire required. To illustrate : We have 22 
amperes to carry a distance of 135 feet and the loss to be al- 
lowed is 3 per cent at 110 volts. We therefore multiply 135 X 
22 = 2970, and turning to table IV., which is figured for 3 per 
cent loss, follow downward in the column under 110 until we 
reach the number nearest equal to 2970, which, in this case, is 
.3180 corresponding to a No. 7 wire. With this wire our loss 
will be slightly less than 3 per cent, while with No. 8 it would 
be somewhat in excess of 3 per cent. 

For three-wire systems using- 110 volts on each side the 
column marked 220 volts should be used. The column marked 
440 volts is provided for three-wire systems using 220 volts 



^34 MODERN ELECTRICAL CONSTRUCTION. 

on each side. The sizes determined will be correct for all 
three wires in both cases. 

The columns at the right, marked motors, are arranged 
in the same way, the only difference being, for greater con- 
venience, they are figured in horse-power feet instead of am- 
pere feet. For this reason we multiply the distance in feet 
by the number of horse-power to be transmitted and divide 
by the percentage of loss, all other operations remaining the 
same as under lights. When any considerable current is to 
be carried only a short distance the wire indicated by the de- 
sired loss will very likely not have sufficient carrying capacity ; 
it is, therefore, always necessary to consult the table of carry- 
ing capacities. 



RULE FOR WIRING TABLES. 

For lights, find the ampere feet (one leg) and under the 
proper voltage find the number equal to this or the next 
larger; opposite this number, in the column marked B. & 
S., will be found the size of wire required. 

For motors, proceed in the same way, using horse- 
power feet instead of ampere feet. 

For alternating currents, the results obtained by multi- 
plying the amperes (or horse-power) by the feet, should 
be multiplied by the following factors: 

1.1 for single-phase systems, all lights. 

1.5 for single-phase systems, all motors. 

For two-phase, four-wire, or three-phase, three-wire 
systems, each wire need be only one-half as large as for 
single-phase systems and the number obtained may, there- 
fore, be divided by two. 



TABLES. 



335 



Resis. 
per 
foot. 


OO-^COrHO Tt<rt<Oi'-icO OiiOCOOSiM r-4 rH r-A CO <0 Ot^rf^O'O 
*V^2S'2!:i2! C3"2'-J'-H(M iOOCO<NO OOcOiOTteO COC^fNC^-iO 
COOCOCCO QOOiOTt<CO (M(Nr-^'-H^ OOOOO OOOOOO 

OOOOO OOOOO OOOOO OOOOO OOOOOO 


1 


o 

> 


o 


Oi-^OOO) 1-HOOQO'^O C«OiTt<t^(N fOi-HiOh-iO t^CSN.iOO^ 

l>. (N 1— 1 lO Tfi (Ni-ht-hoOCO lOOOOiiOO CO O "^ O ■* i-H^ i-h CO r^ cc 

lOt^OS^r^ OOCOOSOO (X)CO(Nt^I> r^t^|>^^ 0^<N(N'*05 

t-Ht-h i-i(NC<lCOTt< lOt^O^Tt^ 00C0OiiO(N 05 O CO O O O 

'I'-H rH C^ (N CO Tjl Tf lO CD l> Tt 00 


1 


OOOOOO 00(NO(X)-^ OOfN-^OOOO OOiMOO CC^^CC^CXX) 

-^OOCTXN 005iOTt<00 (Ni-tOOQOOO Q0C^O5C0t^ Q0(NO(X)t>O 

TjHiOI>CX)»-i rMxMOO^ u^t>.^0'^ TfCOOir-tiO QO -^ OO (N »0 i-i 

.-H rHr-((NC^co rt< lO t>. Oi ^ t}< 00 (N t^ (N t^COOO-^OOr^ 

r-l r-lt-l(N<MCO CO tJ* -^t lO O i-H 


i 


C^OCOtJ<o (NOO-*(NO (MOOOCNC^ OOOCTtHTt (NCOO(NTfH(N 

t-HTt^l^CMOO iOTfCO'-H05 C0(NO5I>t^ (N 00 rf 00 ^ t^ lO tH t^ rt^ Oi 

f-i^rHiMC^ CO-^iOt^OO 'HTtlXNOO ?DiOI>r^i-i Tj< 00 (N ^ T-i (M 

rH,-H^(N(N COTt^iOOX 050(NCOt^'t 

T-i ,-1 ,-( (M »0 


o 

r-l 


OOiO-^J^OO 00(N.-iOO'^ COt^OSOOOO t0»0l>00 00 "^ -^t CO O CO 
(NC0'<^iOt^ 00'HTt<IXN 00":>rt^Or-H O-^COOSCO OrHkOOOOt^ 

rHrHrH(N C^ CO tJH kO t> O) rH t^ O O CO t^ O CO t^ lO 

rH,-l^(N CMdCOCOOCO 

T— ( 






<N -t^ -Tt* -co -co-* ^COOr^t^ Ol>OiCO OOOOOO 
1-t -^ -C^ -co --^lO OI>OSO(N lOt^'-HCOt^. OCOOOiiOw:) 

,-H^ ^^C^<NC^ cococococoo 




^COC^rHO OJOOJ^-OiO tJ<C0C^tHO OOOOO OOOOOO 

too ioo>oooo 

(NCO COTt^TfiOOO 




< 

I 

3 


C3 

s 



> 


i 

'^ 


CO(N<NO«0 O-^OOJOO COdCO-^OO OOOOOO OOO-^-^O-* 
COiOCOOOrH (:DOTjHiOTt< O5C0O51OCO COt^COOO <N00O(NOO 

OOOCOOrH OC0(MC0I> ''tt^^O'O rHCOrHrHrH rJH rt< O CO t^ TfH 

r-l^i-l(N (NCO-^lOO OOOCOO^ l^T^CO^rH rH,-lTH(MCOt^ 

.-H»-HrH(N (NCOTjilOO t^«OiOOO 


CI 


OOOOOOO OfNOOrt^ OOOXr^^t^ OOOOOO'* rt<0(N(NO(N 
f-HC^OTjHiO COO0C^I>.r^ -^CC^fNOO OOXOOO^O T-HTt^cOOiOO 
TjiiOOOOO COO-^OCO (MCOtN.iot^ lO^iOOiO t^ l^ 00 r-t 00 1^ 

rH t-ItH(N(MCO -^lOOXO COl>T-iiOO i0O»O.-HrHC0 

1-1 i-HrHC^(MCO CO"<tTflOOO 


o 

1— ( 


OSCOCOOO OrHOXt^ TjiCO-^Tt^C^ O-^^Ot^ t^OO'-nO-^ 

OOCOC^fN (©-"^OCOOO (NOOI^OO Ol Oi 00 05 1^ lOt^rHOOtNiO 

C^ClCOrJHiO OOOOCOO rH O CO (N CO t^ lO t^ r^ (N 00 fO O lO O 00 

^^^ (NCSJCOt^iO 0000(NO l^OC^iOO-H 

^^^ i-H(NC^(NOO 

l—t 




OO-^OOOO TJH t^ T-H T}< 00 O^iOrHCO XC0O<N<N rHOiCOCO'^QO 

05(N":)010 i-iOOCOOi Ot^OSrHTji (N^O5C0(N rJ<(NC0O5r^^ 

tHtH(NC^ COCOiOOt^ OC^":>OiO (NOOOC^ rJiOOOOO'-; 

^rHrH<MC^ C0"*"5;0t>. 00050(M^OO 

THrHC^rJ* 



886 



MODERN ELECTRICAL CONSTRUCTION. 









.002628 
.002084 
.001653 
.001311 
.001040 

. 000824 
. 000654 
.000519 
.000411 
.000326 

.000259 
.000205 
.000163 
.000129 
.000102 

.000081 
.000064 
.000051 
. 0000431 
.000036 

.0000308 

.000027 

. 000024 

.0000215 

.0000108 

.0000054 




i 

o 





> 


i 


XOOOOOOO (NCOcOOOfN COOOOO-*-* 0<M0rH0 rt^OOrJ^OOiN 
iOtJ<(N^05 -tiCOCOCOtN. ,Ht^QO^(N OOOi'-iOi C0iCC0t^'^(M 
r-iTjHOOCOX CCCO00C0<M |>t^iOiO»0 '^rf'^fNCM OCO'^'-tOiOS 
i-H --H .-1 (M 0< CC-^iOt^CJ tHt^JHoOCOO: I>I>050rtH X(MCCOOr-H 

TH,-lrH(NCM C0Tt^lOI>00 OirHfNTj^OOO 

i-H 1-1 T-H (N iO 





i;DO00(NO COTtHC^JCOOO «DtJ100<£>O OO^CMC^l COOOOOCCKNCD 

OiCMOOJ-^ i-t00rH05O »0<MOI>t>. CO"^XI>0 t^-^c^r^-ioco 

OOr-t-rflxM X^OiCCDi-H OrfiCOi— 101 OiCDOi(M'-i t^ 00 £> >0 i-h CO 

i-i--i^(N (MCCiTt^^I> OirHTf00<M OOO^rJHiO iOcDt^00l>'* 

rHrH,-l(N (N CO -^ lO CO »> X Oi O i-H CO 

»-H CM ■^ 





""^OCMOOO "^(CoOTfCM rf^COCM'^r^ OOOOOX Tfn CM CM -^ 00 Tt^ 

CMOOiO-'^CD 0050qCM05 CO >0 Oi rf Tt< tJH CO 05 CO 00 "^ rH CO rt^ 00 00 

CMCMCOtJHiO l>00i-ir^I> CM 00 »0 lO r^ CM i-^ -^ lO CM 05 l> "^ t-h CM lO 

r-<'-HrH CM CM CO TjH lO t^ Oi »-H CO CO 00 ^ "^ t^ "* 00 

r^y-^^ i-H CM C<J CM IC O 

1— i 




T— ( 
1—1 


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T-H,-l i-fCMCMCOTj^ lOr^OO'H'^JH OOCMOOCOO t^ TJH ^ t^ lO r-( 

^rH rHCMCMCO^t r}H lO CO CO CO r^ 
1-H CM 




CM •!> "«*< -CO -COrt* IOCOOI>1:>. O I> O O O OOOOOO 
1-H .i-f .CM -CO ••^tO C0l>-050CM lOt^^COt^ O CO CO 05 lO iC 

r-*T-i ^^CMCMCM COCOCOOOCOO 

1—1 




•«*<C0CM»-hO OiOOt^^OiO -^COCMrHO OOOOO OOOOOO 
1— 1 1— ( 1— ( T— ( rH OOOOO OOOOOO 

CMCO CC'^rfiioOO 
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Pi 

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CMTtl-^OCM OOOO-^CO CM-^CMOOCD OCMCMOCO COOOOOOOX 
l>OCOCOCO CMCM00005 Oi CO 05 O CO CM lO t^ CM i-h OCDCM-^OO 
COrHCOCOCM COt^Tfir^Tt^ OSTt^OirHrH CO l> CM CO CM OOOiCOCO'^OO 
rHCMCMCOrf lOCOOOOCO CO --h CO -^ CO tJH X CO CM CM CM CM CO rf^ t^ Tt 
rHr-H t-h CM CM CO Tt^ lO CO 00 O CM -^cOOOOOi-H 

rHr-H i-HrHi-lCM'^X 





CO CM CM O CO O^OCMOO COCMCOrJ^OO OCOCOOOO OOO^JHrt^OTf 
COiOCOOO^ OCOTjHiOTf OiCOOSiOCO cor^cocoo cmxcocmoo 
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tHi-Ht-HCM CMCOrJHlOCO OOOCOt^i-H |>rt<COrH,-H r-H,-HrHCMCOt^ 
1-Hr-HrHCM CM CO T^ lO CO t^ 00 05 O O O 

1-H CM Tfi 



1—t 


QOcpcOgoO OCMOcOtJh OOCOOOOOTtn OOOOOOTt^ Tt^OCMCMOCM 
rHCMCO-^uO COOOCMI:^!^ rt^ CO "^ CM 00 00 00 CO 00 lO i-h rj^ CO CO ^O O 

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,H ^T-^cvjCMcO rJHiOCOOOO COt^^iOO iOO^i-hi-hCO 

1-H rHTHCMCMCO CO^Tj^iOOO 

* 1-CM 


10 


COOOCOOO X^CMOOCO OCMOCMCO COCOO^t^Tt^ CM X CO CO X CO 

05^^00 CM050C005 O'^OiCMX iOCnXCOTt^ XiOCOX'<^05 

i-HCMCO'^iO COt^OCM«0 O^rHOO r}^»-<^OTf XC^lCOr^r-iCM 

r-i^—' (NCMCOTt^iO COXOCMTf COOii-HTf^XCO 

^,-tr-t 1-H rH CM CM •^ 05 



TABLES. 



887 















rH 


00 lOOO-^ 






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OSiOCOOi'M 


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Ot-^rHO»0 




^ 


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(NiO^-HC^ 


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CO CM CM C^l tH O 


^ 


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OOcOiOrf^CC 


C^i (M ^ ^ -H 




OOOOOO 




^ 


(N <N l-H T-< T-^ 


OOOOO 


OOOOO 


o o o o o 


o o o o o o 


<4-i 


OOOOO 




OOOOO 


o o o o o 


o o o o o o 






OOOOO 


OOOOO 


OOOOO 


OOOOO 


'^p.'^ppp. 








ixNOr^t^ 


COrt^Tj^C^oO 


Tt t^CM^O 


OJCOiO^iO 


,-<t^^iOOCO 






Q 


COt>CCI>'<t 


OiOiOiOO 


r^oxooo 


050COCMCO 


lOcoioO'-Hoo 






Q 


t^^t^^co 


"^OH>000 


lO -HOC CM CM 


^rHCMCO^ 


oiocot^-^ 00 






i^ 


rHlNtNCC'^ 


loooo'-ico 


t^CMt^iOT}^ 


cOi-iOlu^O 


t^00 050^CM 










»— 1 1— I 


rH CM CM CO -"l^ 


^t^XOCM 


rj< CO 00 rH CM ^ 


fi^ 












y-\ f— ( 


rH^,HCMTf 00 




-^OfNQOO 


-"^COOO-^C^ 


Tj^OCM'^Tt^ 


OOCOOOOO 


Tt CMCM'«tXTf 


. 






TJHQO^OOCO 


(NI>OTt<iO 


00 CO ut) coo 


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cOC0iOXI>"^ 


w 




s 




o 


coo^oco 


(NCCt^^t^ 


lOi— 1 lOCM rf 


Tj^OiOi-i^r^ 


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COt^rHr^Tj^ 


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^ 


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Tj^iocoooos 


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GO 












rH i-H i-H »H CO CO 




COO00(NO 


CD^t (MOOO 


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OOrt<CMCM 


CO 00 00 CO CM CO 




CO(M(NI>'^ 


lO'^OiCOOO 


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CO^ttT^iOCO 


,-( CO -"^ ^ CO r^ 


> 


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COTt^iOCOOO 


ocoo^o 


COCMCOXCO 


OOt^CMCOTl^ 


rt^ lO CO t^ -^ 00 




(N 




^.-HrH(N(M 


coTt^ioooo 


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OOCMCOOi-tCM 


o 




<N 








FHrHrHCMCM 


CM CO CO -^00 CO 


;^ 


















'<^'O(N00O 


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CO CO (N CO t^ 


-^t^T^OUO 


^COi-HOOO 


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t^^coo^ 


^ ^^rHCOt>. 






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I> 00 0:000 






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OC0C0 05 1010 


03 03 








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coco coco CO 


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too 


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rHCM 








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rH tJ< ts. i-H CM 






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1 












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rH 








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rHi-H 1— 1 !M 


cocortcor^ 


05CM»0X-H 

t-lrHrHCM 


lO 00 CM CO CM ""^ 

CM CM CO CO t>. Th 



338 



MODERN ELECTRICAL CONSTRUCTION. 















^ 


00 lOOOTji 


03 




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rHrt<rHCOCO 


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00 CO lO-* CO 


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coococoo 


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o o o o o o 


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o o o o o o 


fii 


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o o o o o 


o o o o o o 






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l:^ 05 CO !M 00 55 
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• 








rH,Hr-H(M<M 


CO -^lO CD 00 


OCOOOTfH 














T-i y-< T-{ r^ C<1 


CM CO CO rt X rH 




(MTjiTjiO(N 


oooo-*co 


(MrH(M00CO 


0<N(MOCO 


COOXXOX 


w 


^ 




t-ocococo 


(M(M00005 


05C0 0iOC0 


(MiOt^C^l^ 


LOCO CM 'i^ O O 


Oh 


w 


O 


CO 1-1 CO CO (N 


COt^TtHt^TH 


05'*05i-HrH 


COt^(MC0(N 


XOCO CO-* X 


S 


o 


(M 


r-l(N(MCOT}H 


lOCOOOOCO 


COi-HCOrt^CO 


TJH X O (M (M 


CM CM CO •* t^ X 


<< 
g 


<N 




rH rH 


rH(M(NCO'=tl 


»0 'X) OO O (M 


Ti^COXOOrH 










r-^T-^ 


1-H T-^ r-l CM Tti X 




CO(M(NOCO 


O^O(N00 


CO C^ CO'* 00 


O CO cC O 00 


XOTf ^OtJH 




O 


CO lO CO 00 1-1 


coco-^io-^ 


05C0OOC0 


CO t^ CO COO 


CMOOOCMOO 


05 


> 


OOOCCCOrH 


CO CO (N CO r^ 


Tt^t^Tt^OlO 


^COrHrHrH 


T}H Tt< o CO r^ -* 


H 




T-H 


^^^rM 


<NC0Tt<iOCO 


OOOCOt^ rH 


I^TflCOrHrH 


^ ^ T-H (>) CO r^ 


^ 




1— I 






rHrH^C^ 


(MCOT^IOCO 


I^ X 05 o o c 


^3 








k 






r^CMTt^ 




(NCOC^lOO 


cooOTt<co(>j 


OTt^OTt^C^ 


(N(MO00 00 


TjH CO CM CM O CI 








05 O5C0 O O 


^ooocoos 


O00 00Tt<t^ 




CO "-H CO r^ 05 05 






i>? 


COrt^cOOOO 


(MlOOlOrH 


oocoo^ 


OJiMCOrHOO 


I^LOCOCOCM LO 






^ 


rH 


i-ItHCSJ(NC0 


"^iOcOOOO 
iH 


(NCOOTt^OO 


COXCOXCOCM 
C0C0'*'*OiO5 

rH 



TABLES. 







o 


y* 00 iOX'* 
OO-^eOi-HO "<t'*05rHC0 O5iOe0O5(N i-ht^tHCOCO Ot^^'-'OiO 
(MQOiOi-HTt c^io,-iT^(M lOOcOClO QOCOiOTfCO C0(MC-JCM^O 
COOCDCOO 00O»OtJhc0 (N (M 1-h rH ,-( oooco oooooo 




w 

, o 

i 

1 


I 

o 


1 


lOOOiOiO lOOOOO 0»00i00 lOiOiOiOiO lOiOiO^OiS 
OifNOOi-^ O0i05(M00 Oi^l>00^ COOIMCOCJ XOiOOt^iOO 
OOOiOt^CSI r-^»OiOT}Hr-i CMO5'^t^00 cCiCl^»Ot^ OQOC'-<C022 
(NCO-^iOt^ Oi^^CCCO 05CO:0XC0 COOOOOiOO lOOcCr-^olS 
rHr-i,-,C^J (MCOrt'iOt^ CD^Ttt^T-i rroO^iOC^ 


o 


ooooo ooooo ooooo coooo oooooo 

TfOfNOOO -rt^^OO-^Oi Tt^OfMrfiTj^ OOOOOOO ^CMCJrfXrt 

(NOO^^CO 005<MCslOi CCiOOiTj^Tji -^OOSOX -^'-^CCrt^OO,^ 

(NC^C0Tt>O t^OOT-^Tt^t^ (NOOiOiOr^ (M^'^iOC^ a>i>rJir^(MS 

r-Hr-iT-i C^CMCOrJ^iO r-OS'-^COO Xr-(rfr>Tt§ 

^^^ rHCM(M(MiOi=- 


o 


ooooo ooooo ooooo ooooo oooooo 
cooxiMO coT^(^^ox otjhxoco oo-^oifN ccxxocmo 

^t^X^-^ l^fNXiOrt^ 01-H05COCO rH 05 1> O l:^ CO fM O X t^ '^ 

,-i,-i r-iOq(MC0rt< iOt>X.-iT}H X(MXC0O t^ r^ ^ t^ lO ^ 

tHtH r-( C<J (M CO rfi rfiCCCOCOt^ 


o 


0>0000 OOiOOO OiOiOOO ^iOiOOO OOOiOOtC 

-•tr^c^x^o TficooosfN lOX'^rtoi oknxxx --^t^r^ococo 

'-HrHC^c^CO '*^l>X'-t Tt<t^(NXiO lO t^ T-H Tj^ T-^ X»0(M0505X 
r-( i-Ht-hCSC^ICO rfiOt^XO i-HCOiOcCCOt^ 

1-H T—l r-H tH »-H CO CD 




Car. 
Cap. 


c^i •!> .tj< .CO -(O^ looot^r^ ot>.o^o oooooo 
i-H -T-t -c^i -co -rriio cci>050<M ioi>i-ieot>- ocoooi^oio 

r-(T-H r-<T-((MC^<M COCOCOCOOO 


1 cdO 


"^COC^i-iO OiXt^cDiO T!HeO<MTHO OOOOO OOOOOO 

C<JCO COtT rfiOOO 


1 

DC 

c 



< 

o 

> 


o 


OOCOCOOX OiMOCO"^ XC£5Xl>rt< OXXOtJH ^^OMfM.^^ 
1-HCQCDrt^iO COX(NI>t^ tJH cD "^ (M X X X O X O '-''^COO^S 

Tt^lOOXO COCDrHCOCO (NCOt^lOt^ lOr-MOlOiO l>l>Xr-lSS5 

^ ,-i,-((MC^CO rt^iOOXO COl>T-iiOO lOOOr-^oo 
1-1 i-It-i(M(MCO COTfrfiC^c^ 


o 


OOOOO ooooo ooooo ooooo oooooo 

OiCOCOOOi lOi-HOXt^ rtHCO'^CO(M OrtirfHOt^ t^OO^iCT 

OOCOC^iM O'^OCOX !MXI>C005 Oi05X05t^ Ol>r-HX(M^ 

(MfMCO^^iO OXOCOC! r-(OCO(NCO I> lO t> t>. (M CO CO Oi ^O 6i 22 

rH,^T-H (N<MC0rt<iO cOXOfNiO t^X(NiCOo 

,-(^^ r-l(M c^ c^ lO T=. 


O 

t-H 
1— ( 


lOiOiOOiO 101000^0 0»0000 OOOOiO iCOOiOiOiO 
rJ^T-icOO'* (NOOOiCO (NT-(t^(MCCi lOl^CSHOX XiOXOr^ir 
OCOCO^CD COC^COCD-^ cOTt<XC0O5 Oi050505CO ^X^^S(N 
i-Hr-*rH(MCM CO^^OcOX OCOCO.-^CO CO(NCOCOCD Oi^rf^-Sci 
r-.-H^(N(N COTMOcOt- XO^C^So 
T-(i— t ,-1 (M iO 


to 


ooooo 00»000 OOOiOiO OiOOOO lOiOiOiOOO 

axNOSO^O t^XOI>05 OiOt^iOr-M rt^COiOOi-i O "^ CD CO r^ -^^ 

^COt^OCM lOOSiO^Oi OC0050I> ^C^Tf^^ C^r^T-W^CO^ 

^^ r-(,-HC^|COCO iOCOt>0(N COO^OC^ (NXN.flooO 

i-^'-H i-iC^l(NCOCO -"t Tf ic CO (M rf 



340 MODERN ELECTRICAL CONSTRUCTION. 

It is often necessary to reinforce mains which have become 
overloaded. It is quite usual though often very mcorrect, to 
choose by the table of carrying capacities a wire of such size 
that the rated capacity of it and the wire to be re-enforced 
shall be equal to the load. Small w^ires have proportionately 
a much greater radiating surface than larger ones and there- 
fore their carrying capacity is proportionally greater. In order 
that a wire connected in parallel with another wire shall carry 

C. M. X a 

a certain current, its circular mils, must be equal 

A 

where C. M. stands for the cross-section of the larger wire in 
circular mils and A for the current to be carried by it, w^hile 
a is the current to be carried by the extra wire. Table No. 
VII is calculated from this rule and shows the size of wire 
necessary to re-enforce another overloaded to a certain per 
cent as indicated in the top row. For instance, a 0000 wire 
overloaded 40 per cent requires re-enforcement by a No. 1 ; a 
No. 3 wire overloaded 20 per cent requires a No. 10 wire. 
Where large wires are re-enforced in this way by smaller ones 
great care must be taken that the larger wire cannot be acci- 
dentally broken or disconnected, since in such a case the whole 
load would be forced over the smaller wire and would likely 
result in a fire. The two wires should be securely soldered 
together. 

TABLE NO. VII. 



Am- 
























peres. 


B. &S. 


10% 


20 


30 


40 


50 


60 


70 


80 


90 


100 


210 


0000 


6 


4 


2 


1 





00 


000 


000 


0000 


0000 


177 


000 


8 





3 


2 


1 





00 


000 


000 


000 


150 


00 


9 


6 


4 


3 


2 


1 








00 


00 


127 





10 


7 


5 


4 


3 


2 


1 


1 








107 


1 


10 


8 


6 


5 


4 


3 


2 


2 


1 


1 


90 


2 


11 


9 


7 


6 


5 


4 


3 


3 


2 


2 


76 


3 


12 


10 


8 


7 


6 


5 


4 


4 


3 


3 


06 


4 


14 


11 


9 


8 


7 


6 


5 


5 


4 


4 



TABLES. 



341 















•3/19 








ein^ oj 9iou 99S ♦srae^ 








-sis 8JlA-99Jq^ UOSipa JO 








silarotds Joi-aJON 






. 


xa 








a S 


o- - - • - 


*>•-*.. 






S"^ 


a 


"•••"*- 






J a 








2 


.2-^ 


:^;^ ::s::«;s^ :«:^;^ 






« 2 


t-lTHNNWO* ^i-I^OJ 




o 


u 








t> 


PQ 






QC 


§^ 






H 


w 


•^c 






D 


1 


2-5 


O^ «. . « . 




9 


^ 


CQ «} 


fl- " " - • 


"'*'•"* 






i'^ 


:^^:^:^^ 


::^;s^ :^ 




a A' 


^i-i(MNNCO iHrHNWl 


D 




.a pu 








0O 






Q 




S=s 






^ 










<J 




s 






QC 




al 


JS 




o 


^ 


1-^ 

So 
« 2 


§: : . : . r r r . 

w'JtH -H (M CI (M rt^ey?r-n-( 


H^ 


o 


PQ 






^ 


s 








CG 


g^ 








o 


vSC 






Q 


> 




o- i - r s 

a 






iH^i^(M(MCC 


)-^ 




HO 






Q 




«'S 












I 


\ \ \ 


: 




















U M 


u^ 








o © 


O M 








^ fcl 


9 








SS 


^a: - 








Amper 
-35 Ami 
■100 
-300 

600 
-1000 * 


II 






















O '-' «0 i-H i-( « 


WoJ.-^ 








--""SSS 


t3 ^^ 














1 







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^ 










3 CO 


o- - 


^ <• 








fl" • 


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w 


as 


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:3^:^ 






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s 2 


tH'HGQ r-li-^ 


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c 

s 




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m 


1 




a- - 


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:^;^:^ :^;s^ 




rn 




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1-^ 1-^ W i—ty—< 








»<=> 




















JU 




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: ^ : 




CU 




(D • 


: ^t/) 




oi 




Si 


0^ 




H 




GQ 0) 


MQ. 




en 




£§■= 


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i — 1 


H 




« 












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GO 


^ 


1.1 

Jo 




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PQ 






J3 



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s?«2 s?« 








s's 






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C3 H 






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Q 






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s: 


w 


z 




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a 


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^ 


^ ^ 


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rH 




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Bars 


























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342 



MODERN ELECTRICAL CONSTRUCTION. 
DIMENSIONS OF COPPER WIRE 





Diame- 
ters in 
Mils. 


Areas in 
circular 

Mils. 

CM.— a^ 


Weights 






1000 feet 


Mile 




0000 


460. 


211,600. 


641. 


3,382. 


.051 


000 


410. 


168,100. 


509. 


2,687. 


.064 


00 


365. 


133,225. 


403. 


2,129. 


.081 





325. 


105,625. 


320. 


1,688. 


.102 


1 


289. 


83,521. 


253, 


1,335. 


.129 


2 


258. 


' 66,564. 


202. 


1,064. 


.163 


3 


229. 


52,441. 


159. 


838. 


.205 


4 


204. 1 


41,616. 


126. 


665. 


.259 


5 


182. i 


33,124. 


100. 


529. 


.326 


6 


162. 


1 26,244. 


79. 


419. 


.411 


7 


144. 


20,736. 


63. 


331. 


.519 


8 


128. 


16,384. 


50. 


262. 


.654 


9 


114. i 


i 12,996. 


39. 


208. 


.824 


10 


102. 


10,404. 


32. 


166. 


1.040 


11 


91. 


8,281. 


25. 


132. 


1.311 


12 


81. 


6,561. 


20. 


105. 


1 . 653 


13 


72. 


1 5,184. 


15.7 


83. 


2.084 


14 


64. 


\ 4,096. 


12.4 


65. 


2.628 


15 


57. 


3,249. 


9.8 


52. 


3.314 


16 


51. 


2,601. 


7.9 


42. 


4.179 


17 


45. 


2,025. 


6.1 


32. 


5.269 


18 


40. 


1,600. 


4.8 


25.6 


6.645 


19 


36. 


1,296. 


3.9 


20.7 


8.617 


20 


32. 


i 1,024. 


3.1 


16.4 


10.566 


21 


28.5 


1 812.3 


2.5 


13. 


13.283 


22 


25.3 


640.1 


1.9 


10.2 


16.85 


23 


22.6 


510.8 


1.5 


8.2 


21.10 


24 


20.1 


I 404. 


1.2 


6.5 


26.70 


25 


17.9 


320.4 


.97 


5.1 


33.67 


26 


15.9 


252.8 


.77 


4. 


42.68 


27 


14.2 


201.6 


.61 


3.2 


53.52 


28 


12.6 


158.8 


.48 


2.5 


67.84 


29 


11.3 


127.7 


.39 


2. 


84.49 


30 


10. 


100. 


.3 


1.6 


107.3 


31 


8.9 


79.2 


.24 


1.27 


136.2 


32 


8. 


*64. 


.19 


1.02 


168.5 


33 


7.1 


50.4 


.15 


.81 


214.0 


34 


6.3 


39.7 


.12 


.63 


271.7 


35 


5.6 


31.4 


.095 


.5 


343.6 


36 


5. 


25. 


.076 


.4 


431.6 



TABLES. 



348 



Table giving the outside diameters of rubber covered wires for use on 
voltages less than 600. 



>si tf^ 


Solid 


Solid 


Strand- 


Strand- 


R K- S 


Wire 


Wire 


ed Wire 


ed Wire 


Gauge 


Single 


Double 


Single 


Double 


Braid 


Braid 


Braid 


Braid 


0000 


47-64 


54-64 


52-64 


59-64 


000 


41-64 


46-64 


48-64 


55-64 


00 


38-64 


43-64 


43-64 


48-64 





36-64 


40-64 


40-64 


45-64 


1 


33-64 


37-64 


37-64 


42-64 


2 


29-64 


33-64 


32-64 


37-64 


3 


27-64 


31-64 


30-64 


34-64 


4 


25-64 


29-64 


27-64 


31-64 


5 


24-64 


28-64 






6 


22-64 


26-64 


24-64 


28-64 


8 


18-64 


22-64 


20-64 


23-64 


10 


16-64 


20-64 


18-64 


21-64 


12 


15-64 


19-64 


16-64 


20-64 


14 


14-64 


18-64 


15-64 


19-64 


16 


10-64 


13-64 






18 


9-64 


12-64 







Solid 
Twin Wire 



54-64x101-64 
46-64X 87-64 
43-64X 81-64 
40-64X 75-64 
37-64X 70-64 



Stranded 
Twin Wires 



64 
64 



33-64X 62 
31-64X 58 
29-64X 54-64 
28-64X 52-64 
26-64X 49-64 

22-64X 41-64 
20-64X 37-64 
19-64X 35-64 
18-64X 33-64 
13-64X 24-64 
12-64X 22-64 



59-64x111-64 
55-64x103-64 
48-64X 91-64 
45-64X 85-64 
42-64X 79-64 

37-64X 69-64 
34-64X 64-64 
31-64X 58-64 

28-64X 52-64 

23-64X 42-64 
21-64X 38-64 
20-64X 36-64 
19-64X 34-64 



Table giving 


the outside diameters of 


rubber covered ^ 


wires for use on 


Voltage 


;s between 600 and 3500. 






Size 

B.&S. 

Gauge 


Solid 


Solid 


Strand- 


Strand- 






Wire 


Wire 


ed Wire 


ed Wire 


Solid 


Stranded 


Single 


Double 


Single 


Double 


Twin Wire 


Twin Wire 


Braid 


Braid 


Braid 


Braid 






0000 


-49-64 


56-64 


53-64 


61-64 


56-64x105-64 


61-64x114-64 


000 


46-64 


53-64 


50-64 


57-64 


53-64X 99-64 


57-64x107-64 


00 


41-64 


46-64 


47-64 


53-64 


46-64X 87-64 


53-64X 99-64 





38-64 


43-64 


42-64 


46-64 


43-64X 81-64 


46-64X 88-64 


1 


35-64 


40-64 


39-64 


43-64 


40-64X 75-64 


43-64X 82-64 


2 


33-64 


38-64 


36-64 


40-64 


38-64X 71-64 


40-64X 76-64 


3 


31-64 


36-64 


34-64 


38-64 


36-64X 67-64 


38-64X 72-64 


4 


29-64 


33-64 


31-64 


35-64 


33-64X 62-64 


35-64X 66-64 


5 


28-64 


32-64 






32-64X 60-64 




6 


27-64 


31-64 


28-64 


32-64 


31-64X 58-64 


32-64X 60-64 


8 


24-64 


28-64 


26-64 


30-64 


28-64X 52-64 


30-64X 56-64 


10 


22-64 


26-64 


24-64 


28-64 


26-64X 48-64 


28-64X 52-64 


12 


21-64 


25-64 


22-64 


26-64 


25-64X 46-64 


26-64X 48-64 


14 


20-04 


24-64 


21-64 


25-64 


24-64X 44-64 


25-64X 46-64 



NOTE. — These figures are taken from data furnished by one of the largest 
manufacturers of wire and are believed to be of at least as great dimensions 
as any standard wire on the market. Judgement must be used in applying 
these dimensions as the same size wire B. & S. gauge, of different makes 
often varies considerably in outside diameter. 



344 



MODERN ELECTRICAL CONSTRUCTION. 



Outside Diameters of Rubber 
Covered Cables. 



Outside Diameters of Weather- 
proof Wire. 



Capacity in 


Diameter 


Cir. Mils. 


over Braid 


1,500,000 


113-64 


1,250,000 


107-64 


1,000,000 


97-64 


950,000 


95-64 


900,000 


94-64 


850,000 


93-64 


800,000 


89-64 


750,000 


87-64 


700,000 


83-64 


650,000 


81-64 


600,000 


79-64 


550,000 


76-64. 


500,000 


73-64 


450,000 


68-64 


400,000 


66-64 


350,000 


64-64 


300,000 


61-64 


250,000 


59-64 



Dimensions of Unlined Conduit. 



Nominal 
Internal 
Diam. 
Inches. 



1 

u 

H 
2 

2i 
3 



Actual 
Internal 
Diam. 

Inches. 



Actual Thick- 
External ness of 
Diam. Walls 

Inches, j Nearest 
t 64th 



17-64 

23-64 

31-64 

40-64 

52-64 

67-64 

88-64 

103-64 

132-64 

157-64 

196-64 



26-64 

35-64 

43-64 

54-64 

67-64 

84-64 

106-64 

122-6^ 

152-64 

184-64 

224-64 



4-64 

5-64 

6-64 

6-64 

7-64 

8-64 

9-64 

9-64 

10-64 

13-64 

13-64 



Size of 


Outside Diameters. 


Wire 


Solid 


Stranded 


1,000,000 




108-64 


900.000 





103-64 


800,000 





100-64 


700,000 


._ 


94-64 


600,000 


. 


85-64 


500,000 





80-64 


450,000 





76-64 


400.000 


— . 


73-64 


350,000 





64-64 


300,000 





62-64 


250,000 


— 


58-64 


0000 


50-64 


55-64 


000 


47-64 


51-64 


00 


39-64 


43-64 





36-64 


39-64 


1 


32-64 


35-64 


2 


30-64 


33-64 


3 


27-64 


30-64 


4 


25-64 


28-64 


5 


22-64 


24-64 


6 


20-64 


22-64 


• 8 


17-64 


18-64 


10 


16-64 




12 


14-64 




14 


12-64 




16 


10-64 




18 


8-64 





Dimensions of Lined Conduit 



Nominal 


Actual 


Actual 


Internal 


Internal 


External 


Diameter 


Diameter 


Diameter 


Inches 


Inches 


Inches 


^ 


32-64 


54-64 


I 


45-64 


67-64 . 


1 


58-64 


84-64 


u 


80-64 


106-64 


1* 


90-64 


122-64 


2 


115-64 


152-64 


2i 


144-64 


184-64 


3 


176-64 


224-64 



TABLES. 
DIMENSIONS OF PORCELAIN KNOBS. 



345 



Trade 
No. 


Height 


Diameters 


Hole 


Groove 


Height of 
Wire 





2\ 


3 


n 


1 


i 


1 


3 


2i 


i. 


f 


n 


2 


2 


2 


i 




1 


3 


If 


2 


^ 


IT 


f 


3* 


2 


2 




^ . 


1 


4 

4i 


1? 


li 


j 


1 


o 


u 


1 




1 


54 


1^ 


i 


4 


TS 


1 


7 


f 


i 


i 


T6 


^ 


9 


u 


1 


A 


A 


1 


lOi 


If 


If 


f 


t 


1 



DIMENSIONS OF GLASS KNOBS. 



Trade 
Number 


Height 


Width 


Size of 
Hole 


Size of 
Groove 


1 

I' 

3 

7 
8 


U 
1| 
If 
2i 
2i 
3f 


U 

1^ 

2 

2 

2 

2f 


3 

8 


-j 

1 

r cable 



SIZES OF PORCELAIN TUBES. 



Internal 


Shortest 


Greatest 


Outside 


Diameter 


Length 


Length 




Inches 


Obtainable 


Obtainable 




^ 


i 


24 


TE 




1 


24 
24 
24 


2 




1 


24 


1^ 


1 


H 


24 


1^ 


li 


2i 


24 


ifl 


U 


24 


24 


2^ 


If 


24 


24 


ift 


2 


2* 


24 


?i 


24 


24 


3A 


24 


24 


24 


m 



DIMENSIONS OF MOULDINGS. 



Size of Groove 


Size of Wire 


Size of Groove 


Size of Wire 


7-32 

5-16 

13-32 

9-16 


14-12 B. & S. 

10- 8 B. & S. 

6-5-4 B. & S 

3-2-1-0 B. & S. 


3-4 

7-8 
1 
1 1-4 


0-0000 Stranded 
250.000 C. M. 
500.000 C. M. 
750.000 C. M. 



34(5 



MODERN ELECTRICAL CONSTRUCTION. 
DIMENSIONS OF CLEATS. 



One-Wire Cleats. 

DuGGAN Cleat. 

No. 4 holds wires 16-8 B. 

6-2 



&S. 



No 
No 
No 
No, 
No, 



2-00 

000-300,000 C. M. 
400,000-800,000 C. M. 
900,000-1,200,000 C. M 



Brunt Cleat. 
Stand. 
Number Width Length Groove 

328 f 2 i holds wires 16-5 B. & S 

329 1 2i i •• " 8-3 

331 \i 21 H - '• 3-00 

330 li 2-h * " '* 4-1 

332 n 21 H •' •• 0-0000 



Two AND Three-Wire Cleats. 
Brunt. 

No. 334 2-wire holds wires T .16-8 B. & S 

No. 337 3 wire " •' 16-8 B. & S 

DUGGAN. 

No. 3 2-wire holds wires 16-8 B. & S. 

No. 2 2-wire " " 6-00 B. & S. 

No. 1 3 wire " '* 16-8 B. & S. 

Pass <fe Seymour. 

No. A-3 2-wire holds wires 14-12 B. & S. 

No. 3 2-wire " " 14- 6 B. & S 

No. A-43 3-wire " " 14-12 B. & S 

No. 43 3-wire " " 14- 6 B. & S. 



TABLES. 
DIMENSIONS OF IRON SCREWS. APPROXIMATE. 



347 



Trade Number 


Diameter in 


Nearest B. & S. 


Greatest Length 


Fractions 


Gauge 


Obtainable 





ik 


15 


1 


1 


lis 


14 


^ 


2 


ii 


12 


1^ 


3 


i^ 


11 


1* 


4 


b\ 


9 


1^ 


5 


^\ 


8 


2i 


6 


t¥s 


7 


3 


7 


^is 


7 


3 


8 


/is 


6 


4 


9 


in' 


5 


4 


10 




5 


4 


11 


bI 


4 


4 


12 


tVb 


4 


6 


13 
14 


# 


3 
3 


6 
6 


15 


i 


2 


6 


16 


H 


2 


6 


17 


s 


1 


6 


18 


^s 


1 


6 



DIMENSIONS OF COMMON NAILS. APPROXIMATE. 



Trade 


Diameter in 


Nearest B. & S. 


Length in 


No. 


Number 


Fractions 


Gauge 


Inches 


per lb. 


2d 


lifi 


13 


1 


875 


3d 


X 


12 


U 


565 


4d 


}^ 


10 


H 


315 


5d 


6i 


10 


If 


270 


6d 




9 


2 


180 


7d 


St 


9 


2i 


160 


8d 


t/i 


8 


2h 


105 


9d 


ZiH 


8" 


2f 


95 


lOd 


19 


7 


3 


70 


12d 


T5^B 


6 


3i 


60 


16d 


T 


.6 


3i 


50 


20d 


i¥b 


4 


4 


30 



Fine Nails 



348 



MODERN ELECTRICAL CONSTRUCTION. 



RATING OF MOTORS. 
Full Load Currents. 



H. P. 


110 VOLTS 


220 VOLTS 


500 VOLTS 


1 


1.9 


.95 


.42 


A 


2.7 


1.35 


.62 


^ 


5. 


2.50 


1.15 


1 


7.5 


3.75 


1.70 


1 


9.2 


4.60 


2.10 


2 


17.5 


8.75 


4. 


3 


24.6 


12.30 


5.60 


4 


32. 


16. 


7.50 


5 


40. 


20. 


9.20 


7h 


57. 


28.5 


13. 


10 


76. 


38. 


17.5 


15 


110. 


55. 


25. 


20 


144. 


72. 


34. 


25 


176. 


88. 


40. 


30 


210. 


105. 


49. 


35 


250. 


125. 


57. 


40 


280. 


140. 


65. 


45 


320. 


160. 


75. 


50 


350. 


175. 


80. 


60 


430. 


215. 


100. 


75 


520. 


260. 


120. 


100 


700. 


350. 


160. 


125 


880. 


440. 


210. 


150 


1056. 


530. 


245. 


175 


1230. 


615. 


280. 


200 


1400. 


700. 


325. 



RATING OF INCANDESCENT LAMPS. 





1 10 VOLTS 






220 VOLTS 




c. p. 


Watts 
18 


Amperes 


C. P. 


Watts 


Amperes 


4 


.16 


8 


36 


.16 


6 


24 


.22 


10 


45 


.20 


8 


30 


.27 


16 


64 


.29 


10 


35 


.32 


20 


76 


.35 


12 


40 


.36 


24 


90 


.41 


16 


56 


.51 


32 


122 


.55 


20 


70 


* .64 


50 


190 


.86 


24 


84 


.75 








32 


112 


1.00 








50 


175 


1.60 









TABLES. 



349 



The Hewitt-Cooper Mercury Vapor lamp requires a current of aV)out 3.. 5 
amperes. 

The Nernst lamp consumets 88 watts per glower; for a. 6 glower, 110 volt 
lamp, about 4.8 amperes. 

Series miniature lamps, operated 8 in series, on 110 volts, require a current 
of about .33 amperes for 1 candle power lamps, and 1 ampere for 3 candle 
power lamps. 



Tables showing the currents which will fuse wires of different sub- 
stances. 



B. &S. 
Gauge 


Diam. 


1 

Copper 


Aluminum 


Germar^ 
Silver 


Iron 


10 
12 
14 


102. 
81. 
64. 


333. 
236. 
165.7 


246.5 
174.4 
122.8 


170. 
120.5 
84.6 


102.3 
72.6 
50.9 


16 
18 
20 


51. 
40. 
32. 


117.7 
81.9 
58.5 


87.1 
60.7 
43.4 


60.1 
41.8 
29.9 


36.1 
25.2 
18. 


22 
24 
26 


25.3 

20. 

16. 


41.1 
28.9 
20.7 


30.5 
21.5 
15.3 


21.0 

14.8 
10.6 


12.4 
8.9 
6.4 


28 
30 
32 


12.6 
10. 

8. 


14.5 

10.2 

7.3 


10.7 
7.6 
5.4 


7.4 
5.2 
3.7 


4.5 
3.1 
2.3 


34 

36 


6.3 
5. 


5.1 
3.6 


3.8 
2.7 


2.6 

1.8 


1.6 
1.1 



INDEX. 

Acid fumes 89-161 

Alternating current system 35 

Amperes : 13 

Arc lamps, construction of 283 

Arc lamps, installation of 127-132-197 

Armored cable, construction of 249 

Armored cable, installation of 168-173 

Armored cable, metallic sheaths to be grounded. . .95-173 

Attendance 69 

Auto-starters 78 

Balancing coils on three-wire systems. (See Reactive 
Coils.) 

Base frames, generators and motors 47-73 

Batteries, storage and primary 27-89 

Bells 19 

Bell wires 288 

Blocks at fixtures and switch outlets 150 

Bonds, rails in car houses 234 

Boxing, where necessary 131-158-235 

Burglar alarms 288 

Burrs and finns, fixture work 190 

Bushings at entrance to building 94-289 

Bushings for wires 1 16-255 

Bushings, lamp sockets 196 

Bus bars 60-63 

Cabinets, construction of 125-127-148-177-275 

Cabinets, use of 125-144-147-177 

Cabinets for rheostats and auto-starters 78 

Cable, armored 249 

Calculation of wires 40 

Canopy insulators 187 

Car wiring and equipment 225 

Car houses 233 

Care and attendance 69 

Carrying capacity table 332 

351 



352 index: 

Ceiling fans 87-189 

Ceiling rosettes, construction of 276 

Ceiling rosettes, use of 145 

Central stations 47 

Changes in rules 302 

Choke coils - 67 

Circuit breaker, construction of 264 

Circuit breaker, installation of 50-76-84-88-124-134-146 

Circuit breaker, how high may be set 146 

Circuit, open 9 

Circuit, closed 9 

Circuit, divided 16 

Circular mil 40 

Cleats 256 

Compensator coils 198 

Concealed wiring 116-151-155-158 

Concentric wire 248 

Condensers 286 

Conductors 10 

Conductors. (See Wires.) 

Conduits, installation of 174 

Conduits, metal, construction of 250 

Conduits, wire for 248 

Conduit work 166-174 

Constant current systems 32-121 

Constant potential systems 33-134 

Converters. (See Transformers.) 

Convertible wiring systems 143 

Coulomb 13 

Crane wiring 319 

Crossing of constant potential pole lines over 5,000 

volts 98 

Currents 7-13 

Currents for motors 75-328 

Cutout cabinets. (See Cabinets.) 

Cutouts, construction of 264 

Cutouts, installation of 124-134-145 

Cutouts, must protect all wires of the circuit 124 

Damp places 121-126-161-193 

Decorative lighting systems 198 

Distance between conductors, inside 131-159-168-235 

Distance between conductors, outside 91 

Divided circuits 16 

Drip loops at service entrance 94-137 



INDEX 85.S 

Dynamo rooms 47 

Economy coils 198 

Electric bells I9 

Electric gas lighting 293 

Electric heaters 152 

Electrolytic corrosion of underground metal work.... 96 

Electrolysis 96-1 18 

Electro-magnetic devices for switches 134 

Electro-motive force 11 

Electro-plating 10 

Elevator shafts, wires in 123 

Equalizers 64 

Extra high potential systems 236 

Fan motors hung from ceilings 87-189 

Feeders, railway 233 

Fished wires 156-168 

Fittings and materials 238 

Fixtures 187 

Fixtures, canopies 187 

Fixture v/ire 247 

Fixture wiring 173 

Flexible cord, construction of 244 

Flexible cord, construction of, heaters 246 

Flexible cord, construction of, pendants 244 

Flexible cord, construction of, portables 245 

Flexible cord, use of 195 

Flexible tubing, construction of 257 

Flexible tubing, where permitted 168 

Foreign currents, protection against 288 

Formula for soldering fluid 113 

Fuses, construction of 269 

Fuses, installation of 134-145-327 

Fuse protection for generators 50 

Gas lighting, electric 293 

Generators 47 

Ground connections 103-182 

Ground connections for transformers 104 

Ground detectors 61-69 

Ground plates, construction of 108 

Ground return wires, trolley systems 96 

Ground wire for lightning arresters 67-288 

Grounded trolley circuits 96 



'^5^ INDEX 

Grounding interior conduits 182 

Grounding low potential circuits 106 

Grounding of dynamo and motor frames 47-73 

Grounding sheaths of cable 95 

Grounds, testing for 69 

Guards, irons or wires, use of 93-96-98 

Guard strips, inside work, where required 131-158 

Hanger boards, construction of 282 

Hanger boards, when not used 133 

Heaters, electric 152 

High constant potential systems 234 

Incandescent lamps as resistance 66-198 

Incandescent lamps in series circuits 134-236 

Incandescent lamps, where inflammable gas exists. ... 193 

Induced currents 26 

Induction coil 25 

Inside work 110 

Insulated platforms at high potential machines 47-73 

Insulating joints, construction of 283 

Insulating joints, when required 187 

Insulation of fixture canopies, when required 187 

Insulation of trolley wires 96 

Insulation resistance 71-294 

Insulators 10-111 

Insulator spacing, inside work 131-159-168-235 

Interior conduits. (See Conduits.) 

Joints in conductors 94-112 

Joints, insulating. (See Insulating Joints.) 

Junction boxes 174 

Junction boxes, conduit, installation of 174-183 

Knob and tube work 110 

Knots in flexible cord required in sockets and rosettes. 196 
Lamps, arc. (See Arc Lamps.) 

Lamps, incandescent, rating of 328 

Lightning arresters, construction of 287 

Lightning arresters, installation of 66 

Lights from trolley circuits 234 

Loop system * 169 

Loss in voltage 36 

Low potential systems 155 

Lugs for terminal connections, when required 

113-259-266-268-284 



INDEX 355 

Magnets 9 

Marine work 295 

Mechanical injury, protection against 131-158-235 

Mercury vapor lamps 314 

Mils, definition of 40 

Motors 73 

Motors, enclosure for 86 

Moulding, construction of 254 

Moulding work 156-163-186 

Moving picture machines 293 

Multiple-series systems 85 

Neutral wire 33 

Ohms 12 

Ohm's law 13 

Oily waste 69 

Open wiring , 159 

Outlet and switch boxes, construction of 252 

Outlet boxes or plates, conduit, when required. ... 173-179 

Outline lighting 316 

Outside work 91 

Panel boards, construction of 274 

Picture moving machines 293 

Pole lines 95 

Pole line, constant potential, over 5,000 volts 97 

Pole lines, high pressure, near buildings 102 

Portable conductors 195 

Portable lamps, installation of 195 

Power 14 

Power from trolley circuits 234 

Power, transformer and switch stations 47 

Protection for gas outlet pipes 187 

Protective devices on signal circuits, construction of. .291 
Protective devices on signal circuits, installation of... 289 

Practical hints 323 

Railway power plants .' 88^ 

Railway wires. (See Trolley Wires.) 

Reactive coils 286 

Receptacles. (See Sockets.) 

Reinforcing wires 142 

Resistance 12-17-41 

Resistance boxes. (See Rheostats.) 

Resistance for arc lamps, low potential 198 

Rheostats, construction of 284 

Rheostats, installation of 64-78 



H5(5 INDEX 

Roof wiring 92 

Rosettes, construction of „ 276 

Rosettes, use of 145 

Running boards, construction of 158 

Sag in outside wires 93 

Series arc system 32-127 

Series incandescent lamps 236 

Series-multiple system 35-85 

Service blocks and wires 91 

Service switches 146-148 

Service wires, underground 123 

Signaling systems 288 

Sockets, construction of 278 

Sockets, installation of 193 

Soldering fluid, formula 113 

Soldering stranded wires 113 

Spark arresters, construction of 283 

Spark arresters, when required 132-198 

Speed controller 83 

Square mil 40 

Starting boxes 64-78 

Static electricity, overcoming 50-73 

Stations and dynamo rooms 47 

Storage battery rooms 89 

Switchboards 62 

Switch boxes, conduit, construction of 252 

Switches, construction of, knife 258 

Switches, construction of, snap 261 

Switches, electro-magnetic 134 

Switches, flush, installation of 150 

Switches, installation of 146 

Switches, when may be single pole 76-148 

Switches, time 127 

Systems, alternating current 35 

Systems, constant current 32-127 

Systems, constant potential, general rules 134 

Systems, extra high constant potential 236 

Systems, high constJint potential 234 

Systems, low^ constant potential 155 

Systems, multiple-series 85 

Systems of wiring 32 

Systems, series-multiple 85 



INDEX 357 

Systems, signalling 288 

Tables 335 to 349 

Tablet boards 274 

Telegraph, telephones and other signal circuits 288 

Telephones 23 

Testing 69-190-323 

Theater wiring 199 

Three-wire system 136-143-155-324 

Transformers, grounding of secondary 107 

Transformers, installation of, inside 90-103-235 

Transformers, installation of, outside 103 

Transformers, oil and air cooled 315 

Transformer stations 47 

Transmission, electric 36 

Transmission lines, constant potential, over 5,000 volts 97 

Tree system of wiring 139 

Tricks of the trade 330 

Trolley wires 96 

Tubes, insulating 1 16-255 

Underground conductors 123 

Vacuum tube systems 314 

Volt 11 

Voltmeter, switchboard, circuit for 61 

Waterproof construction 161 

Waterproof pendants 194 

Watt 15 

Wire, concentric 248 

Wire conduit 248 

Wire, construction, general rules ' 238 

Wire, fixtures 247 

Wire netting required on arc lamps 132-168-198 

Wire, rubber covered 238 

Wire, slow burning 243 

Wire, slow burning, weatherproof 242 

Wire, weatherproof 243 

Wires, calculation of 40 

Wires, car work 225 

Wires, carrying capacity table 332 

Wires, central station 60 

Wires, concealed knob and tube work 168 

Wires, conduit work 166-248 

Wires, constant current systems 127 

Wires in parallel 142 

Wires in stations and dynamo rooms 61 



358 INDEX 

Wires, number in conduit 328 

Wires, extra high potential 236 

\Vires, finished * 156-168 

Wires, fixture work 247 

^Vires, low potential, general rules 155 

Wires, high potential 234 

W ires, inside, constant current 127 

Wires, inside, general rules 110 

Wires, moulding work 163 

Wires, open work, damp places 161 

Wires, open work, dry places 159 

Wires, outside, overhead 91 

Wires, service 91 

Wires, signal 288 

Wires, trolley 96 

Wires, underground 123 

Wiring systems 32-143 

Wiring tables 333 



THE KING OF ALL— The Companion Volume to Modern 
Wiring Diagrams— ^ust from the Press 

Eieciricai Wiring si!^ 
Construction Tatties 

By Henry C. Horstmann and Victor H. Tousley 

Contains hundreds of easy up-to-date tables covering everything on 

Electric Wiring. Bound in full Persian Morocco. 

Pocket size. Round corners, red edges. 

PRICE, MET, $1,SO 

Partial Table of Contents 

This Book contains 

among others: 

Tables for direct current 

calculations. 
Tables for alternating cur- 
rent calculations. 
These tables show at a 
glance the currents re- 
quired with any of the 
systems in general use, 
for any voltage, effici- 
ency, or power-factor, 
and by a very simple 
.©alculation (which can 
be mentally made), also 
the proper wire for any 
loss. 
Tables showing the small- 
est wire permissable 
with any system or num- 
ber of H. P. or Hghts 
under "National Electri- 
cal Code" or Chicago 
rules. Very convenient 
for contractors. 
Tables for calculating the 

most economical loss. 
Tables and diagrams 
showing proper size of 
conduits to accommo- 
date all necessary combinations or 
number of wires. 
Tables and data for estimating at a 
glance the quantity of material re- 
quired in different lines of work. 

l\ S this is intended for a pocket-hand-book everything that would 
-^ makes it unnecessarily cumbersome is omitted. There is no 
padding. Every page is valuable and a time saver. This book will 
be used every day be the wireman, the contractor, engineer and 
architect. All parts are so simple thai very ''.ttle electrical knowl- 
edge is required to understand them. 

S3nt, all chrages paid to any address, t^pon receipt of price. 




FREDERICK J. DRIiKE I CO., Publishers, 



Chicago 



DYNAMO TENDING 




ENGINEERS 

Or, ELECTRICITY 
FOR STEAM ENGINEERS 

By HENRY C. KORSTMANN and 
VICTOR H. TOUSLEY, 
Authors of "Modern Wiring Diagrams and 
Descriptions for Electrical Workers." 



This excellent treatise is \NT:'itten by 
engineers for engineers, and is a clear 
and comprehensive treatise on the prin- 
ciples, construction and operation of 
Dynamos, Motors, Lamps, Storage Bat- 
teries, Indicators and Measuring Instru- 
ments, as well as full explanations of the 
principles governing the generation 
of alternating currents and a descrin- 
tion of alternating current instruments and machinery. There are 
perhaps but few engineers who have not in the course of their labors 
come in contact with the electrical apparatus sue! as pertains to light 
and power distribution and generation. Vt the present rate of increase 
in the use of Electricity it is but a question of time when every steam 
Installation will have in connecton with it an electrical generator, even 
In such buildings where light and power are supplied by some central 
station. It is essential that the man in charge of Engines, Boilers, 
Elevators, etc., be famiiiarwith electrical matters, and it cannot weli 
3e other than an advantage to him and his employers. It is with a view 
to assisting engineers and others to obtain such knowledge as will enable 
them to intelligently manage such electrical apparatus as will ordinarily 
come under their control that this book has been written. The authors 
have had the co-operation of the best authorities, each in his chosen field, 
and the information given is just such as a steam engineer should koow, 
To further this information, and to more carefully explain the text, 
nearly 100 illustrations are used, which, with perhaps a very few excep- 
tions, have been especially made for this book. There are many tables 
covering all sorts of electrical matters, so that immediate reference can 
be made without resorting to figuring. It covers the subject thoroughly, 
but so simply that any one can understand it fully. Any one making a 
pretense to electrical engineering needs this book. Nothing keeps a nian 
down like the lack of training; nothing lifts him up as quickly or as 
surely as a thorough, practical knowledge of the work he has to do. This 
book was written for the man without an opportunity. No matter what 
he is, or what work he has to do, it gives him just such information 
and training as are required to attain success. It teaches just what 
the steam engineer should know in his engine room about electricity. 
13mo, Cloth, 100 Illustrations. SizeSV^x?^. PRICE NET A I l?|| 
Sold by booksellers generally, or sent, all charges paid, upon wliOU 
receipt of price 

FREDERICK J. DRAKE & CO., Publishers 

CHICAGO, ILL. 



Easy Electrical Experiments 
and How to Make Them 

By L. P. DICKINSON 

This is the very latest and m^s'' 
valuable work on Electricity for th< 
amateur or practical Electrician pub. 
lisned. It gives in a simple and 
easily understood language every 
thing you should know about Gal- 
vanometers, Batteries, Magnets, In- 
duction, Coils, Motors, Voltmeters, 
Dynamos, Storage Batteries, Simple 
and Practical Telephones, Telegraph 
Instruments, Rheostat, Condensers, Electrophorous, 
Resistance, Electro Plating, Electric Toy Making, etc. 
The book is an elementary hand book of lessons,, 
experiments and inventions. It is a hand book for 
beginners, though it includes, as well, examples for 
the advanced students. The author stands second to 
none in the scientific world, and this exhaustive work 
will be found an invaluable assistant to either the 
Student or mechanic. 

Illustrated with hundreds of fine drawings^ printe<^ 
on a superior quality of paper. 

I2mo Cloth* Pficct $t*25o 

Sent postpaid to any address upon rcceiDt of pric 

'iiEDERICK J. DRAK£ & CO., Publishers. 

CHICAGO, ILL. 




ALL TECHNICAL TF/RMS AVOIDED 



Practical Telephone Hand Book and 
Guide to Telephonic Exchange 

HOW TO CONSTRUCT AND MAINTAIN TELEPHONE LINES 



By T. S. BALDWIN. M. A. Illustrated. 

Containing chapters on "The Use 
of the Telephone, Series and Bridg- 
ing Phones, Line Construction, Ma- 
terials to be used, Locating and Cor- 
rection of Faults in Instruments 
and Lines." 

This is the best book ever published 
on Farm Telephones and has been 
the sensation of the past year in 
telephone circles. It is the only book 
ever issued which treats the subject 
exhaustively and comprehensively. 
It is of inestimable value to promot- 
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contains all of the arguments that are 
necessary to show the advantages oi 
rural party lines. It also tells how 
such lines should be constructed and 
cared for. 

The great growth of the telephone industry during the past 
few years, and in response to the demand for a comprehensive 
feook, giving a clear, terse idea of the different principles govern- 
ing the construction, installation, care and management of the 
various telephones and their appliances, the Practical Telephone 
Hand B©ok has been compiled. It is written in a most clear and 
careful style and aims to give a complete review of the subject of 
telephony. 

No expense has been spared in gathering valuable information, 
and it has been the aim of the author to make this treatise the most 
complete elementary book ever written on this subject for all per- 
sons interested in this great achievement of modern science. 

The text is profusely illustrated by cuts of commercial appa- 
ratus and carefully prepared diagrams of circuits. No diagram is 
given without a full explanation. The apparatus and methods used 
in making all the tests required in commercial telephone work, ia- 
cluding the exchange, are fully treated. 

Price, $1.00 Postpaid. 
FREDERICK J. DRAKE & CO. 

CHICAGO. 




JUST THE BOOK FOn BEGINNERS AND ELECTRICAL WORKER» 

WHOSE OPPORTUNITIES FOR GAINING INFORMATION ON 

THE BRANCHES OF ELECTRICITY HAVE BEEN LIMITED 

ELECTRICITY 

Made Simple 

Bt claek cabyl haskins 

A BOOK DEVOID OF 

TECHNICALITIES 

SIMPLE, PLAIN AND 

UNDERSTANDABLE 

There are many elementary books about 
electricity upon the market but this is 
the first one presenting the matter in 
such shape that the layman may under- 
stand it, and at the same time, not writ- 
ten in a childish manner. 

FOR ENGINEERS, DYNAMO MEN, 
FIREMEN, LINEMEN, WIREMEN AND 
LEARNERS. FOP STUl Y OR 
REFERENCE. 

This little work is not intended for the instruction oi experts, nor as 
a guide for professors. The author has endeavored throughout the book 
to bring the matter down to the level of those whose opportunities for 
gaining information on the branches treated have been limited. 

Four chapters are devoted to Static Electricity ; three each to Chemi- 
cal Batteries and Light and Power; two each to Terrestrial Magnetism 
and Electro-Magnetism ; one each to Atmospheric Electricity ; Lightning 
Rods; Electro -Chemistry; Applied Electro - Magnetism ; Force, Work 
and Energy; Practical Application of Ohm's Law; also a chapter upon 
Methods of Developing Electricity, other than Chemical. 

The large number of examples that are given to illi^rate the practi- 
cal application of elementary principles is gaining for it a reputation as 
a text book for schools and colleges. 

In reviewing this book an eminent electrician says of it : 

"All that 999 men out of 1000 want to know can be imparted in plaia 
language and arithmetic. I therefore think that such a book as jouta 
Is the kind that does the greatest good to the greatest number." 

I2mo, Cloth, 233 Pages, IO8 Illustrations Cfw /\/\ 
=z=z=zz=i: PRICE JVet ipl^VV 

For Sale by booksellers generally or sent postpaid to any 
address upon receipt of price, 

FREDERICK J. DRAKE & CO., Publishers 

CHICAGO, ILL. 




THE MOST IMPORTA^^T rJOOK ON ELECTRICAL CONSTRUCTION 
WORK FOR ELECTRICAL WORKERS EVER PUBLISHED. 

REVISED AND ENLARGED EDITION 

MODERN WIRING 

DIAGRAMS AND DESCRIPTIONS 

A Hand Book of practical diagrams and 
information for Electrical Workers. 

By HENRY C. HORSTMANN and 
VICTOR H. TOUSLEY 

Expert Electricians. 

This grand little volume not only telb 
you how to do it, but it shows you. 

The book contains no pictures of bells, 
batteries or other fittings; you can see 
those anywhere. 

It contains no Fire Undv^rwriters' rules; 
you can get those free anywhere. 

It contains no elementary consider- 
ations; you are supposed to know what 
an ampere, a volt or a "short circuit" 
is. And it contains no historical matter. 

All of these have been omitted to make 
room for "diagrams and descriptions" 
of just such a character as workers need. 
We claim to give all that ordinary elec- 
trical workers need and nothing that they 
do not need. 

It shows you how to wire for call and alarm bells. 

For burglar and fire alarm. 

How to run bells from dynamo current. 

How to install and manage batteries. 

How to test batteries. 

How to test circuits. 

How to wire for annunciators; for telegraph and gas lighting. 

It tells how to locate "trouble" and "ring out" circuits. 

It tells about meters and transformers. 

It contains 30 diagrams of electric lighting circuits alone. 

It expiams dynamos and motors; alternating and direct currents. 

It gives ten diagrams of ground detectors alone. 

It gives "Compensator" and storage battery installation. 

It gives simple and explicit explanation of the "Wheatstone" Bridge 
and its uses as well as volt-meter and other testing. 

It gives a new and simple wiring table covering all voltages and all 
losses or distances. 

16mo., 160 pages, 200 illustrations; full leather binding, 
round corners, red edges. Size 4x6, pocket edition. PRICE 

Sold by booksellers generally or sent postpaid to any address 
upon receipt of price. 

FREDERICK J. DRAKE & CO., Publishers 

CHICAGO, ILL. 




$1.50 



Practical Telephone Testing 

By W. G. and D. R. MIDDLETON 




w 



'HILE many of the tests incorpor- 
ated in this book have hitherto 
been treated technically, this 
work explains in detail the practical 
methods in common use and in such a 
way that the men in charge of apparatus 
and lines can readily understand and 
make the tests. 

A detailed description is given of Tele- 
phone and Telegraph lines, circuits and 
apparatus and of the principles and use 
of modern testing equipment. 

The errors commonly made in testing 
are guarded against and the reasons for 
using certain methods for speed, accuracy 
and the elimination of errors, are fully 
shown. 

Information indispensable to the wire 

chief, including the testing of Toll and 

Rural lines and Magneto, Central Battery 

and Automatic Switchboards is given. All 

standard testing apparatus is illustrated 

in detail so that there is no chance of 

failure in following the instructions. 

There is a chapter on the calibration of instruments and several 

chapters are given to cable testing, presenting original and unpublished 

methods of locating faults. 

The chapter on voltmeter testing is well worth the price of the book 
and no one in charge of electrical lines or apparatus should be without 
a copy. 

An effort has been made to present the matter in logical sequence so 
that even the inexperienced reader can successfully make valuable 
fault locations. 

The book was written after years of practical experience and situa- 
tions commonly encountered are outlined. It is profusely illustrated 
with photographs of apparatus, circuit drawings and diagrams of 
tests. These drawings are so made that the principles of the tests are 
obvious and in many cases it will not" be necessary to refer to the text. 
Formulas have been simplified and each step of the derivation is 
carefully explained. A little practice in the manipulation of testing 
apparatus after a thorough comprehension of the principles set forth 
in this treatise will satisfactorily equip one for testing work. 



Sold by bookseHers generally or sent postpaid 
to any address upon receipt of price :: :: :: 

IGmo. Full Leather. Round Corners. Red 
Edges. Pocket Size :: :: :: :: Price, $1.50 



FREDERICK J. DRAKE & CO. 



PUBLISHERS 



CHICAGO. ILLINOIS 



ELEMENTARY ELECTRICITY 

UP TO DATE 

By SIDNEY AYLMER-SMALL, M. A. I. E. E. 




THIS book opens up the way for 
anyone who desires an accurate 
and complete knowledge of elec- 
tricity as a useful agent, in the hands 
of man, for the transmission of me- 
chanical energy, and the creation of 
hght. 

In addition to opening up the way 
as referred to above, the book also 
serves as a guide and instructor to the 
seeker after knowledge along these 
lines. 

Beginning in the form of a simple 
catechism on the primary aspects of 
the subject it conducts the student by 
easy stages through the various as- 
pe'cts of static electricity, the different 
types of apparatus for producing it, 
all of which are plainly described and 
illustrated and their action made plain and easy of comprehension. 
Quite a large space is devoted to this important topic, although no 
more than is actually necessary, as the subjects of condensers and simple 
electrical machines are also thoroughly handled, and the principles 
governing their action clearly explained and illustrated. The subject of 
atmospheric electricity is next dealt with, and lightning arresters treated 
upon, especially in their relation to electric power stations, sub-stations 
and line wires. The wonderful and mysterious subject of magnetism 
is next treated upon at length and clearly explained— the explanations 
being accompanied by illustrations. 

Primary batteries of all types, storage batteries and the effects of elec- 
trolysis each and all receive a large share of attention. Electric circuits 
and the laws governing the flow of current, including Ohm's law, are all 
clearly explained. The student has now arrived at the point where 
electrical w^ork, power and efficiency is the topic, and where the genera- 
tion and transmission of electrical currents of high potential and large 
volume are explained. 

Sold by booksellers generally or sent postpaid to any address upon receipt of price. 
12mo. Cloth, 500 Pages, Fully Illustrated : Price, $1.00 



FREDERICK J. DRAKE & CO. 

PUBLISHERS : : : : CHICAGO, ILLINOIS 



THE AUTOMOBILE HAND-BOOK 

OVER 100,000 SOLD 

By ELLIOTT BROOKES. Assissted by Other Weil-Known Experts 

Revised and Enlarged 1911 Edition— The largest and most practical 

work publishedo Used by all up-to-date automobile schools as 

their everyday text- book. 16mo, over 650 pages and 

over 320 illustrations. Full Leather Limp, Round 

Corners, Red Edges. Price, $2.00. 

At the present time nearly all automobile 
troubles or breakdowns may, in almost 
every case, be traced to the lack of knowl- 
edge or carelessness of the owner or opera- 
tor of the car, rather than to the car itself. 
The automobile hand book is a work of 
practical information for the use of owners, 
operators and automobile mechanics, giv- 
ing full and concise information on all 
questions relating to the construction, care 
and operation of gasoline and electric auto- 
mobiles, including road troubles, motor 
troubles, carbureter troubles, ignition 
troubles, battery troubles, clutch troubles, 
starting troubles. With numerous tables, 
useful rules and formulae, wiring diagrams 
and over 320 illustrations. 

Special efforts have been put forth to 
treat the subjects of ignition, and igni- 
tion devices, in a manner befitting their 
importance. A large section has been 
devoted to these subjects, including bat- 
teries, primary and econdary, magnetos, 
carburators, spark plugs, and in fact all devices used in conneciion with 
the production of the spark. Power transmission is thoroughly discussed, 
and the various systems of transmitting the power from the motor to the 
driving axle are analyzed and compared. 

The perusal of this work for a few minutes when troubles occur, will 
often not only save time, money, and worry, but give greater confidence 
in the car, with regard to its going qualities on the road, when properly 
and intelligently cared for. 

A WORD TO THE WISE 

The time is at hand when any person caring for and operating any 
kind of self-propelling vehicle in a public or private capacity, will have to 
undergo a rigid examination before a state board of examiners and secure 
a license before they can collect their salary or get employment. 

Already New York State has enacted such a law and before long, wi'h 
a positive certainty every state in the Union will pass such an ordinance 
for the protection of life and property. 

Remember this is a brand new book from cover to cover, just from 
the press — 1911 Edition — and must not be confounded with any former 
editions of this popular work. 

Sent prepaid to any address upon receipt of price 

FREDERICK J. DRAKE & CO., Publisher i 

1325 Michigan Avenue, - - - CHICAGO, U. S. A. 




MAY 20 »911 



The Automobile Mechanician's 
Catechism 

Over 400 Questions and 
Answers. Illustrated with 
three large folding charts 
with all parts fully and 
correctly numbered. 

By 
CALVIN F. SWINGLE, M. E. 

Pocket Edition, 16mo. Full Leather, 
Round Corners, Red Edges, Stamped 
in Gold. Over 100 Pages. 

Price, $1.25 

Adapted for use in the technical 
school, the work shop, or on the road. 
The questions asked and the answers 
given in this catechism w^ill be found 
to be an indispensable guide to quick- 
er and better work by the automobile 
student, no matter whether that work 
be in the school, the shop, on the 
road or before the examining board of 
engineers. 
The subject matter is not made up of cuts and advertisi-^g 
eulogies from the catalogues of manufacturers and dealers, but 
consists of a plain, practical course of instruction, containing at 
the same time sufficient theory to enable the student to become 
thoroughly familiar with the basic principles controlling the 
design, construction and operation of modern automobiles of ad 
types, whether gasoline, electric, or steam driven. The questions 
and answ^ers have been carefully compiled, and they are presented 
in a clear and concise form, covering every detail of automobile 
work; a reliable instructor and assistant to the student and 
mechanician, while to the chauffeur the book is a most valuable 
guide and helper, giving correct meihod for handling the machine 
under all conditions of service, and what to do in case of break- 
downs. The demand for skilled mechanics in the fie d of automo- 
bile w^ork is constantly increasing, and especially so regarding the 
operation of the machines, quite a number of the states and larger 
cities a'ready having rigid laws requiring chauffeurs to undergo a 
strict examination before a board of mechanical experts before 
being licensed as automobile chauffeurs or drivers. 




Sent prepaid to any address upon receipt of price. 



FREDERICK J. DRAKE & CO , Publishers 

1325 Michigan Avenue - - CHICAGO, U S. A. 




One copy del. to 



f^^y 2hmi 



LIBRARY OF CONGRESS 

III 

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